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Timing lights

Points (both old camshaft nose type & canister types)

Ignition modules; original, changes, updates

New coil style changes

NOTE: Information on ignition timing versus piston movement has been moved to item #18 at:

Dyna & other points boosters

Spark plug suppressor caps; also see:

Coils:  specifications, failure modes, testing

Ignition canisters, repairing, etc.

Dyna, Boyer & other ignitions

Testing &  troubleshooting

High idling rpm

Hall sensors

Rubber seal strip at points cavity, pre-1979 models


Copyright, 2014, R. Fleischer 
article #30

There are THREE major ignition system articles on this website.  You are reading article #30.  You will NOT get a complete understanding without reading ALL THREE.  The other two are: #28 & #29.     #31 & #32 may ALSO be of interest.


For further information, see Haynes, Clymer's, or other manuals.  Be cautious for errors in those manuals. They are only "fair" on ignition items & testing, & certainly not good for repairs to the innards.

RECOMMENDED:   The CHITECH BMW Electric School Manual, still available at $30.  The description on their website does not quite do justice for all that is in this manual.  Written by super-guru, OAK Okleshen!    
For a critique of that manual:

In-depth information on spark plugs and their caps:

Timing lights:

Many decades ago, timing lights consisted of a lamp bulb containing neon or argon gas, which was attached to the spark plug & to engine ground, via two well-insulated cables. This type worked fine, needed no power from any battery, but was not very bright, but OK for a somewhat darkened garage area. There have been folks who use this method to light-up a small fluorescent lamp.  These methods are all obsolete, although they DO work.  A lot of old-time mechanics got electric shocks using these.

The next type of timing light had car radio 'vibrators' (vibrating electrical contacts) to produce the A.C. needed for input to a transformer, the output of which was high voltage, which was rectified to D.C. and applied to contacts inside a smallish glass 'flash tube' that contained a somewhat pressurized gas. The high voltage circuit included a fairly powerful capacitor that could supply large sudden and very short time period currents, repetitively for a fraction of a second, to supply the flash tube power.  Triggering of the flash tube was obtained in various ways, typically a few turns of wire was wrapped around the outside and high voltage applied to create a strong electric field.  That caused the power supply, with its capacitor, to discharge into the lamp via the lamp end contacts. 

Next came timing lights that had internal transistorized oscillators instead of the vibrator. These soon were updated to include transistorized amplifiers, so now NO high voltage connection to the spark plug wiring was required, just an adjustable opening 'clamp probe', that contained a coil of wire or other sensor means, to trigger the transistor amplifier, which, in turn, triggered the lamp discharge.  The result was a convenient tool for shop and home, with no chance of an electrical shock.

The glass flash tube produced a short intensely bright white light for each spark plug spark event. The design and circuitry can be made so that the flashing is both reliable & bright, even at hig rpm.  This type is the most common.

A further development was the type that has a rotary dial, in which degrees of advance, sometimes retard, can be dialed-in for special purposes ...this can be helpful when certain types of timing marks are not easily gotten-to.  This type can be confusing, and I do NOT recommend its use, unless you already have one & KNOW how to use it.   This type is absolutely not needed for Airheads use, and that includes stock single plug ignition as well as dual plugging, and, AFAIK, to any aftermarket ignitions.  If you are purchasing a timing light, and are the more nerdy type, you might want this type with a dial for timing degrees. 

There are types of timing lights that include circuitry that will actually enable dwell time to be measured.  Dwell time is, put simply, the period of rotational degrees during which the ignition coil is being magnetically charged, compared to its time of not-being-charged.  Contrary to some beliefs and statements, DWELL TIME measurements ARE NOT very important to AIRHEAD ignition.

Timing lights are available that do not need external power sources, that means that the timing light needs no connection to the vehicle battery, but uses an internal battery.   That can have a POSSIBLE advantage besides not needing the vehicle battery.  The possible advantage is that in rather rare situations, using the vehicle battery to power the timing light can cause irregular timing indications.  Usually this is in a system with a poor higher internal resistance battery, or other fault, so engine ignition pulses are seen at the battery terminals.  Note that the very earliest timing lights, with just an argon lamp connected directly to the spark plug wire connection, also did not need external power.  The same can be said for those using lamps with similar UNsafe connections.

About the use of a timing light powered by the vehicle battery:
In most instances, this works well; that is, using the vehicle battery for timing light power, which is commonly done and usually OK.   A very rare instance is when the timing light itself produces electrical noise, upsetting the timing reading. Less rare is when some other problem exists in the vehicle causing strange timing light indications at the flywheel (clutch carrier on 1981 and later models).  This can be from such as a bad battery; poor connections; or, in some instances just slightly higher connection resistance at some places in the vehicle OR there is electrical noise from a poor diode in an alternator diode board, etc.   If some form of electrical noises, including delayed ignition impulse noises, feed back to the timing light, at its battery connection, the timing light can be irregular.  All these things are reasons that SOME mechanics power their timing lights from an EXternal battery.  So ...there is a POSSIBLE problem with reading the timing marks clearly and accurately, if the timing light is vehicle powered. This CAN happen, but almost always does NOT. The possibility is why BMW recommends using an EXternal power source for the timing light.  The external timing light power source could be almost any 12 volt battery that can power the timing light.  Any problem usually shows up as somewhat irregular and unstable timing light indication at the timing marks.  Since unstable timing marks are USUALLY due to timing chain and guides and sprockets wear, or irregularities at ignition points, if there is any question of accurate timing, DO try an external battery instead of powering your timing light from the vehicle under test.

Here is a bit more about false timing light 'information':

Any sort of electrical noise at the battery terminals where you have connected the timing light ... can, but does not have to, ...cause false triggering.  Some timing lights are much more susceptible to triggering on electrical noise INCLUDING faulty ignition pulses at the spark plug ignition wire.  False triggering can make it more difficult to determine which of multiple images on the flywheel (or clutch carrier) is the correct one. Multiple images on the flywheel are QUITE COMMON and usuallycome from irregularities in the bike's own ignition triggering, almost always from jerking-about of the timing chain, and NOT problems with the timing light.  Irregularities in a points drive can be MECHANICALLY caused from run-out at the end of the camshaft (especially up through 1978).  Irregularities with the 1981 and later electronic ignition timing might come from the mechanical drive to the canister, but it is usually the chain, guide/tensioner and sprockets.  The POINTS canister model of 1979-1980 is more stable than the older points-at-end-of-cam models, but the 1979-1980 is less stable than the electronic ignition of 1981 & later.  It is very easy to see the instabilities with a timing light. Try an external battery.  If any difference, then always use an external battery with that timing light.

While the best thing is to power a timing light from an external battery, quite frankly I seldom do that myself! ...unless I am specifically looking into a problem situation.

I suspect that most all of you will use a timing light that triggers via a clamping probe over the insulated ignition wire, and that has no advance/retard dial. It works fine on our Airheads, no matter if single plug, dual-plugged, one coil or two coils, aftermarket or stock ignition.

On an after-market split ignition, like the separately cylinders-adjustable Dyna unit used on the early points type motorcycles, you must set the timing for both cylinders individually. Theoretically this produces a more accurate, less jittery ignition timing.  In practice, that MAY be true, but usually is fairly modest in effect.

Points amplifiers, sometimes called points boosters, are made by a small number of manufacturer's.  They will GREATLY increase points life.  Accel was a popular brand; and Dyna still makes a unit that has been popular for a very long time.  These are two of the popular makers, but kits are available from others, and may have some advantages, with ability to handle lower primary ohms coils and possibly produce better sparks and reliability may be better.

There are KITS to put together your own points booster/amplifier:  Also, Arcade electronics; and maybe others. Velleman is probably the actual maker of all these, sold by others, using model number 2543.  A problem could occur if you have coils that draw more amperes than any of the points booster amplifiers are rated for, 4 amperes for the Dyna Booster. Many have used that booster in that overloaded condition, if they are kept reasonably cool.  AFAIK the Velleman is rated at 4 amperes, but with the heat sink that comes with it, I think it will handle MORE, if placed in a relatively cool place on the motorcycle;  ...someplace under the fuel tank? I think you could also install a more powerful transistor ....have not yet tried that; haven't a Velleman kit here to play with.

NOTE:  if you wish to build a points booster from scratch, that is, it is NOT a kit, I have put the schematic diagram for a good one in the following article.  This one can power even the lowest primary ohms coils:

Even with a points booster/amplifier, you MUST keep the points cam faintly lubricated, or it will wear fast, & may even squeak.  The points must be clean and dry!

NEVER open the points manually very much; opening them quite wide might weaken the spring.

The NON-canister Airheads have points located on the forward (nose) end of the camshaft in a small engine cavity.  The lower points screw head is very close to the points spring, and if a wrong screw or washer is use, the screw can contact the spring and the points are effectively shorted, and you get no ignition.  This is seen now and then right after someone replaces the points and can't understand why the engine will not start.

The NON-canister models points connection wire goes from the points cavity through a rubber grommet which often gets displaced when working in the area.  DO NOT replace the cover until the wire & grommet are in proper position, or you could cut the wire when replacing the cover.   You can use a strong adhesive on the grommet.   The BMW price for that grommet will cause you to have an empty wallet.

The NON-canister models (pre-1979) have a groove around the points cavity. The groove contains a necessary rubber O-ring (or, seal strip), which was made in two thicknesses.  The thicker one may not fit.  These have two part numbers in the books.  These come in lengths you cut to fit.  Install them after cleaning them AND the groove with acetone or MEK and a small metal bristle brush.  Put small droplets of cyano-acrylic glue (Crazy Glue, etc....the GEL form is better) in the cavity groove, before installing.   Push a few times into position if need-be, THEN cut with an Xacto knife, fitting/cutting so the ends are together snugly; and let sit overnight, after which you CLEAN with acetone or MEK.  Smear a faint amount of  grease (silicone dielectric grease is best) on the surface, before replacing the outer cover....and TAKE CARE that the rubber grommet is installed properly and fits the cover as you install it.  The seal strip:
11-14-1-265-394 is supposedly 3.2 mm, used until 1974.
11-14-1-262-644 is supposedly 4.2 mm, used after 1974.
If you were to order either, you probably will get the 394.  Maybe.

HINT!  You can use a Classic K bike oil filter cover O-ring, which is 11-13-1-460-425.  You can even install a used one! (CLEAN it with a strong solvent first ....get rid of the oil! ...or, just purchase a new O-ring).  Thanks to Tom Cutter for the hint!

CLEAN the points by rotating the engine until they are closed (so are pressured by the points spring blade) and then opening them by hand ONLY A SMALL AMOUNT, just enough to slide a piece of paper between the points.  Absorbent paper of some sort, but not a linty paper towel.  I use a non-glazed business card or common printer paper, etc.   FIRST ut a couple drops of a fast drying solvent on the small piece of paper.   Acetone is fine (NOT wife's oily based acetone). That will eliminate any oil film layer on the points. You do not want to file the points because that removes the special metal layer on them.
 The points are expensive, so you may decide to file them anyway when they get worn a fair amount, even if their life is further reduced.  If you have to file them because there is a pronounced tit and valley on the points, do it only lightly, and use a fine grit points file or thin flat jewelers file.  Keep the tool square to the points and do not pressure the points much.   I have used diamond or carbide grit impregnated METAL fingernail 'boards', and they work fine too.

Be sure to lubricate the cam felt (none in canister points models) and lubricate the cam, SLIGHTLY, with any good high temperature grease.  Check the points every 5,000 miles for gap, clean and refresh the grease, and check timing.   DO NOT OVER- LUBRICATE! do NOT want grease or oil to get into the points gap!

Be sure the points cavity area is clean and dry; pay attention to the rubber grommet and wire as you put the front cover back on the bike.  I will assume the seal for the cavity is good & intact.

The above advice generally also applies to the canister points models of 1979-1980.

Ignition points/ATU/etc:

The ATU (Automatic Timing Unit) is discussed, in depth, at
SEE ALSO, item 5., well below...

ADDITIONAL information, especially about a high rpm idle problem, is treated in this article, a number of paragraphs below.

CONDENSER:   0.2 microfarad

DWELL:   This is covered in depth in:

Ignition points as used in the Airhead canisters (1979 and 1980 Airheads models), ETC:
Unconfirmed data: Bosch on Mitsubishi Colt (69-80 6 cyl), some VW (Bus to 1972 for instance); Volvo, some Toyota, Ford Cortina TD and TF, 6 cyl Falcom XY and XD, ....etc. Old VW points springs may be too weak, and cause floating problems.  NOTE: Porsche & some others, used Bosch GB752, which had a slightly higher spring tension, so less tendency to have floating problems at VERY high, ~red-line area rpm.  DO NOT willy-nilly install those points. BMW has a stronger spring points unit for the canister ignitions, it solves a problem seen, if rarely, with misfiring at & above 6500 RPM.  The part number, which was finally adopted for all the canister points models (I think) is:  12-11-1-243-969.   This item can be differentiated from the softer spring model by the color of the WIRE, which should not be black, but black with white rings.  In Europe, BMW made other changes at the same time to this canister, changing the vent hose to a white colored one (12-11-1-243-920), and the cover went to 2 hole mounting.

The 01-011 VW points may fit the canister (number may be shown as 01011). Those points have a more standard spring tension, use a fiber rubbing block.  If you were using very high rpm all the time, racing, or?, you might want 01030 which has a stiffer spring & plastic rubbing block.

The 1979 & 1980 Airheads had canisters with points & did NOT have a felt pad to help keep the points cam lubricated.  If the lubrication on these or earlier points cams dries out, the rubbing block & the cam can make loud chirping noises. This indicates that the rubbing block is wearing fast; soon the points will have no opening, & the bike will quit running. Remove the outer lid (2 screws) & lubricate the cam sides VERY sparingly....with a high temperature grease...or, real ATU greases from Bosch. Put one drop of a decent oil on the outrigger bearing if the canister model.  NOTE that the points can NOT be adjusted properly withOUT the outrigger bearing in place. DO NOT open the points manually beyond what is needed ....doing so will cause them to loose spring tension and you can then have ignition abnormalities.

NON-canister points, that means Ignition points for 1970-1978 Airheads:
BMW has shipped wrongly made points sets, made in China.  They did that under part number 12-11-1-243-555.  The rubbing block is too long & you cannot get proper timing, etc.   I suggested the Noris points from such as Beemershop, etc.   BMW has recently been shipping 12-11-1-243-556, which fit & work OK.  The requirements for lubricating the points cam as with the canister type points models (1979-1980) are the same for the older models, and, for those older models, the shaft (cam end) needs lubrication too.  DO NOT open the points manually beyond what is needed. Older models have a felt as part of the points assembly; it should be kept faintly lubricated.   Before the 1979 introduction of the canister, Airhead motorcycles all had points ignitions with felts; the felt AND cam required lubrication (both on the engine cam's shaft inside the ATU, and the ignition cam outer surface).  Since the automatic advance unit was at the cam tip (not buried as in the canisters), the automatic advance unit cleaning and lubrication could be done rather easily; with two types of Bosch greases used, one for the rubbing block, one for the area between automatic advance and cam ....and the shaft.

I DO lubricate the canister cam in the 1979-1980 canisters that have points, & I do it very lightly.  There is no felt in most if not all point sets for these canisters.  Lubricating the cam LIGHTLY (you may have to clean it first) certainly extends points life, & is easy to do.  More serious work on the canisters requires more difficult disassembly.

Rotating the points plate CLOCKWISE in pre-1979 models will retard the spark.

High Idle RPM (usually after warmup, usually QUITE high, towards 2000:
This is primarily a problem with the ATU mechanism in the CANISTER models.  It is possible for the old style ATU to have such problems, but cleaning and lubrication and inspecting for slacked springs, is easy, and does not need a lot of explanation.

High idling rpm, perhaps slowly worsening (?), is caused by several possible problems.  Sometimes more than one of these problems at the same time.

1.  An internally "sticky" automatic timing unit in the ignition canister at the front of the engine.   I discuss how to determine if this is the problem and how to fix it, at 7.

Do it yourself, cleaning and lubrication of the ATU:

Overhaulers?    Tom Cutter,   Tom's garage is located in Yardley, PA
Shop:  (215) 321-7944

Other overhaulers are listed considerably down this article, in its own section.

Another group of photos on how to clean and lubricate the ATU:

2.  Leaking: intake stubs; throttle shafts; hoses/clamps... intake stubs to carburetors.

3.  Mal-adjusted carburetors (usually the idle mixture screw).

4.  No slack in one or both throttle cables; or, no slack in the top cable on three cable models.

5.  Weak or stretched/sacked automatic advance springs.  This is not difficult to determine; a visual look-see will show one or more of these conditions:  
(a) The springs do not fully bring the advance weights back to engine stopped position.  Usually there is a wee bit of play BEFORE the springs expand (if you move the weights manually). 
(b) The idle timing may vary more than normally. 
(c) The timing RANGE is likely OK, but RPM at which maximum timing is reached is much lower than expected.
Source for automatic advance springs:

6.  Carburetors wrongly assembled, or other problems.  This includes leaking DOMES; leaking throttle shafts (see item 2); pulled-inwards parts of the enrichener gasket; WRONGLY assembled enrichener discs or lever assemblies; & WRONGLY stamped L or R (by Bing factory!!) enrichener shafts.  Photos of the proper and improper assembly is in my carburetor articles.

7.  Perhaps THE most common problem, if the jump in rpm is quite large:  sticky automatic advance unit (ATU) IN THE CANISTER MODELS ...resulting in a high idle speed due to excessive timing advance, typically after a full warm-up of the entire engine.  A full warm-up takes at least 10 miles.  You MUST have the ENGINE CASE hot, NOT JUST THE CYLINDERS.  

The PROPER fix is to disassemble the canister & clean & re-lubricate it.  That is not all that easy for the novice.   Sometimes simply removing the oval side plate (you can do with the canister STILL IN THE BIKE!) & squirting in some cleaner &/or a fine oil (NOT EVER WD40!) will help, but may ...or may not ...hold up over time.   When disassembling the canister, which is a bit tricky, some of the ATU parts may need to be burnished (sort of a more complete polishing with a VERY fine sandpaper or silicon carbide paper) which DOES help.   Typically a careful cleaning & polishing by such a very fine paper, finished by light lubrication, IS going to fix the problem.

There are several TESTS for PROVING that the ATU is at fault for a high idle rpm after full warmup (rare, before full warmup):

(a)  Make sure that there are no vacuum leaks at the intake rubber hoses.  To do this, start the engine, let it idle (OK to be somewhat above idle to keep engine running, if doing it with a cold engine; should not be needed with warm/hot engine), & spray brake cleaner or other solvent at the intake hoses, both ends of them at both L & R cylinders.  NO rpm change should be noted in these tests...nor the next ones.  IF any RPM or sound changes, tighten the band-clamps at the hoses between carburetors & cylinder heads & re-check.   It is possible for a hose to deteriorate and tightening will not help, so replace the hose if that is found.

(b)  Next, spray at the throttle shaft linkage area where the throttle shaft exits the carburetor. If the internal throttle shaft O-ring is bad, you will have to disassemble the carburetor to replace it.

(c)  Make sure that there IS free play in the throttle cables; that there is NOT a wrongly adjusted idle mixture screw.

(d)  In some instances, just turning off the engine & restarting it after it was already hot & exhibiting the very high idle, provides enough force to 'reset' a stuck ATU from the inertia of beginning ATU rotation try that.  If that then shows a normal idle, it IS likely an ATU problem.  A few repeats, & if this is the situation, you can be nearly 100% sure it IS the ATU needing attention.

If restarting doesn't show up the problem, then DO get a friend's help.  First take the bike for a 10-20 mile ride, & if the idle rpm went quite high after a WARMUP of the ENGINE CASE, then pull the bike up to a nice big solid object, like a brick building.  You could also just use the brakes.  With the bike in first gear, idling nicely, & no throttle, let out the clutch very slowly, which loads the engine, slowing it.  Slow it to ~900 rpm.  

Have your friend use a timing light, triggered from a spark cable by clamping the sensor pickup over the cable. Have him point the light at the timing hole near the oil dipstick. If the timing is quite well-advanced & not where it should be AT THIS SLOW IDLE (~S mark) the ATU IS THE PROBLEM.  Prove it by pulling in the clutch have a very high idle rpm again, yes?   Try several times.

You could have slacked or otherwise weakened ATU springs.  Easy to test for, use eyeball & the timing light.  Source for automatic advance springs:

Assuming you have fixed the high rpm problem & all is OK:
FIRST, KNOW the valves are properly set, as tight valves will mask all your analysis & work; timing is correct, AND, no vacuum leaks, or other problems.  Now you will re-sync the carburetors.  During the re-synchronization, pay special attention to the idle mixture screw, idle balance, & ending idle rpm (1000-1100).  Many do NOT set the idle mixture screw properly.  If set improperly, the idle RPM can vary considerably from cold, or just barely warmed, to fully hot engine!   Start with the idle MIXTURE screw further out than factory or Bing or other manual such as Haynes or Clymers says initial adjustment should be.  From that further out point, SLOWLY screw inwards, until engine rpm PEAKS & then a wee bit more & the rpm falls off.  Back the idle mixture screw off SLIGHTLY to the exact peak.  Back it off an additional 1/8th of a turn.  If you made changes of any type, go back & forth until ALL carburetor adjustments are such that NO improvements can be made.  If you take more than a few minutes for all this, either ride the bike to cool the engine a bit; or use fans blowing on the cylinders.  This website has an article that describes how to get an appropriate squirrel cage fan for nothing.

See the following article for how to adjust carburetors:

A RARE, but super-annoying problem to find, but a simple fix:
BMW electronic ignition Airheads that typically would idle OK, but won't raise rpm properly.    This problem acts somewhat similarly to a hole in one or both carburetor diaphragms.

The actual problem is a poor ignition kill switch at the bars. Just cleaning that switch may (or may not) fix the problem.  Bypassing the switch WILL show whether or not the problem is that switch.  This fault has driven even some senior technicians NUTS trying to find the problem. I first ran into this situation, & finally identified it, after a lot of labor, a very long time ago.  I eventually used an oscilloscope to find the problem.  I found that an ohmmeter or voltmeter, for rather nerdy-techy reasons, might well not measure ANY fault.    It is RARE, but when it happens to YOU, & you have the bike at your favorite repair shop, you can expect a HUGE amount of labor ...and maybe a lot of 'guessing & shot-gunning' of parts replacements.   Try what I suggest!  If it is YOUR problem, you will be thanking me!

A not so rare problem:
Intermittent ignition failures on 1981 and later can come from the Hall Effect element aging or partial failing, but one thing should be checked first, and that is to remove the bail wire from around the connector that the three wires fasten to, and clean the connections with a hand-shaped pencil eraser, ETC., then coat them with Caig DeOxit, then re-assemble.  I actually do that, then pull apart, and coat a second time, before final assembly and reinstalling the bale wire.

TESTING for failures in the stock BMW/Bosch ELECTRONIC ignition canisters.
+ Sources of information/parts for Airhead ignitions, ETC.

No sparks? ...want a SAFE test for that condition?:

Remove a spark plug. SECURELY fasten the threaded metal body to a cylinder or head fin. You can use a bungee cord for this. I prefer to use a screen door or sash spring, so as to give a bit of added safety, as the spark plug body metal MUST be grounded! Leave the spark plug cap connected to the spark plug. Next, disconnect all battery negative terminal wires. Remove engine front metal cover. Reconnect battery. If you have an EnDuralast permanent magnet alternator, you need not disconnect the battery before removing the front engine cover.

The three pin connector that connects the three-wire plug from the canister to the bike wiring has a thin wire bale clip around it.  That bale clip MUST be removed before you try to unplug the connectors from each other.  Pry an end of the bale wire clip, or both ends, with a tiny tool, & then carefully remove that bale wire clip, don't overly widen its springy-ness.  THEN unplug the connectors.    The 3 spade connectors in these male & female plugs are known to get very minor corrosion, sometimes invisible.  Cleaning with an eraser & then a slight poof of contact cleaner-treatment, will likely fix the problem.  Just disconnecting & reconnecting the connector halves may be enough wiping friction on the connections to make a good contact again.

Be sure KILL switch is centered.  See if the engine now has sparks at that secured spark plug during cranking; ....if so, you had some corrosion on the connector spades, or, there is a temperature problem perhaps.

If STILL no spark, disconnect the two halves again. Use a bent metal paper clip (or whatever) insert it into the center connection on the engine side connector. Turn on the ignition, be sure KILL switch is centered to 'run' position. Repeatedly touch the paper clip to the engine case, which grounds the center connection. You should see sparks at the spark plug (darkened room may help).  If none, you have problems in the module or power to it, or an open coil primary. If you DO get sparks, you have a bad canister Hall device. Don't lose the bale wire clip; reinstall it after you push the connectors back together, before you button up the front cover.

There is also a very useful & different quickie test for the system (does not test the Hall device):  With the ignition on & spark plugs/caps properly grounded as before; simply turn the KILL switch on & off a few times: each time you should get a spark.   That tests the module and coil(s), etc...not the Hall element.   If you get sparks, and not from cranking, your problem IS the Hall device.

Hall device failure: 
Often, but not always, seen as a complete failure, these Hall transistor have been known to become intermittent with temperature changes.  USUALLY, but NOT always, the Hall problems occur after a thorough engine warm-up; the ignition gets intermittent, or dies; and often recovers after the engine cools some.  In some instances, the ignition can fail for a few seconds only. You can usually test the Hall device for temperature problems by going for a ride, and having a can of Cool-Spray or similar with you.  If it normally takes perhaps an hour of or whatever for the engine to be restarted, & if you cool the canister enough  & fairly quickly (It can take a LOT of cooling) ...& then the engine starts up OK, you almost for sure have a Hall device problem.    The devices are replaceable, but BMW only sells the complete canister, VERY pricey indeed....but with this article YOU can repair them, or send them to someone who can!    ALWAYS check the ignition module located beneath the fuel (unless latest riveted type on the later heat-sink)to be sure it has good heat sink paste under it.  Failure to have good condition heat sink paste under the module will allow it to overheat, usually not too long after the bike is started; the ignition typically acts up or totally quits, until the module cools down. After enough of these overheating occurrences the module WILL FAIL.

Here is a link to a source for the entire ignition plate with the Hall devices, ready to go.  This may well be what YOU might want to install:  Search for ignition "trigger assembly black box" or something like that.  The part number is  07912 for the ignition plate with Hall device.    Motobins also has entire canisters for sale.

Euromotoelectrics has repair kits...the plate with Hall element and wire/plug, etc.  ($$$).

BMW is also now selling repair kits ($$$$).

Sources for just the Hall elements in the USA seem to be disappearing.  They are available from Chinese sources, limited feedback shows them working OK.  Here are some sources and information on the electronics canisters:

R-Bike Electronic Canisters, by Pete Serrino;

Troubleshooting Ignition Trigger, as posted to the BMW Airhead Boxer mailing LIST, on 19 April,2001, by John W. Snider.

Ignition Trigger Repair Bulletin, by David A. Braun.
   Long ago I was accused by him of plagiarism. After some correspondence, he agreed that I had NOT, & my information pre-dated his. I am listing the URL here, because it is useful; I do NOT hold a grudge, nor any ill-feelings.  I only mention this incident because some things about this got published for a brief time, & published things tend to last forever on the Internet, whether or not someone sees any follow-ups.

You can also refer to the archives of the Airheads LIST and IBMWR.

Hall device:  Honeywell (MicroSwitch) part #2AV54.
Reported other sources:   Siemens HKZ101 ....available from  in Australia as ZD-1900.  

I suggest you do some diligent searching & compare prices from the various sources.
It has been reported to me that Tom can be slow in shipping the Hall elements.  That may be old news now. There is information on Hall testing here too:

A Chinese source of the original number:

I have seen these advertised, but have not yet tried them.  Hall-Effect Vane Sensor BBHME56 (replacement for sensors 2AV54, 2AV16A, 2AV51A, 2AV56, 2AV63, and similar parts)

The Honeywell device, in case you try to find it on the Honeywell website, can be difficult to find.  That is usually because its official name on that site is  "Hall Effect Vane Position Sensor".  You can TRY using this:  You will still have to mess around to find the correct page. Honeywell constantly plays with location addresses in its website.  You don't need to go find it, unless very nerdy, because I have all the needed information, and more, right here in this article.

UNconfirmed information is that the Hall units may be found in 1979-85 VW; 1978-1983 Audi; 1979-1982 Porsche; and that Bosch 1237011052 may be the number.

***I have thought about recommending that everyone obtain a replacement Hall device; before they stop making them. ??? 

Below is what the Hall sensor looks like. Red, power; black, ground; green, signal.

OLDER units had the sensor plates screwed together; the rivets were hollow; later plates were a push fit, solid rivets.  Some replacement parts use softer rivets, which are easier to remove.

FOR THE NERDY:    Above is a schematic of the Hall Effect device.  Note that the output is an NPN transistor with open collector. Here is a link to an article on diagnosis & repair of the Oilhead Hall Effect ignition sending unit, with some  explanations & details that may help you understand the Airhead electronic ignition .....& how to work on them:

Boyer versus Lucas Rita Ignition:
There are also ignition articles on the website you are reading this on, specifically comparing the Boyer and Lucas Rita, and others.

For the Boyer-Bransden ignition:   See much later for more information.

MODULES (a very long section, covering everything about them for your motorcycle):

Stock Ignition modules:
Common ignition problems (1981 & later, except riveted modules) include failure to clean & renew the heat sink paste under the Module under the fuel tank at reasonable intervals.  If the heat sink paste is old and dried out, the Module will tend to overheat & cause ignition problems after the bike has been on the road awhile; and too many overheating cycles will result in module failure. 

There is more than one location place for the ignition module on the Airheads (1981+) depending on the MODEL OF AIRHEAD & the YEAR.   The 1981-1985 R80G/S, 1983-1984 RT80ST, 1981 to 1987 R65, 1982 to 1984 R65LS, 1985 to 1987 R80 and R80RT, & the other bikes from 1988, all have the ignition module on the right side of the frame backbone tube under the fuel tank & are just behind the IGNITION COIL.  All other earlier models have the ignition module located directly under the tank on a flat aluminum plate, attached where the old ATE brake master cylinder from the seventies was located.  Modules that are fastened by screws to the attached plate can be unfastened by those screws in order to clean the bottom of the module & the plate, before applying fresh heat-sink paste, which MUST be done every year or two.

Listed here are reported modules that MAY work OK.   The word MAY is being used here, because there MAY be complications,
particularly if you have the later 0.5 (often called 0.7 ohm) twin tower coils.  It is my belief that just about any module would be acceptable for emergency use....but may not work properly, so are only recommended, if even that, for emergency use. 

Bosch 0227-100-116.
GP Sorensen 11-5064.
NAPA (Echlin) TP100 (supposedly from Globe Motorist, but will not sell small quantities; Napa prices were vastly higher, but worth another look).
Standard Motor LX501.
Wells Mfg  RB100. 

MANY cars use similar modules.  They may not be same for logic (& timing??), but probably will at least function.  Don't leave the key on for long periods of time with engine not started.

Transpo BM-300 Rocky Point    Also has #9604, Ignition Module, made in the USA.   Has Part number 9608, Ignition Module, made in the USA, for the K bikes.  Also sells the Boyer-Bransden Ignition.  A Microdigital ignition advance curve is later in this article.

VAG (VW and Audi) ignition module part nr. 191 905 351b  is a drop-in replacement for the earlier Airhead modules.

Cars that you may find modules on in wrecking yards, or can get modules at auto-parts stores:

VW Golf and Passat 1979-1989.
VW T2 Transporter and Jetta 1979-1992.
VW Scirocco 1979-1995.
VW Corrado 1979-1995.
Audi 100 1980-1993.
Audi  80 1979-1993.
Audi Coupe 1981-1994.

AGAIN, not that I do NOT recommend aftermarket modules!...although some might be OK for the NON low-ohm coils.

The Ignition Modules (under the tank modules) were initially made in two versions.  On these earliest modules, a spark 'could' occur when the key was first turned on; later versions fixed that (but, the KILL switch could do it, and many of us find THAT convenient during testing).   One of the two early versions was for the kickstart bikes and the other version was for the no-kickstart bikes.  These early modules SUPPOSEDLY had a timing feature that cut off the current flow through the module and coil(s) AFTER about 5 seconds for the kickstarter-equipped bikes & about 1 second or so for the NO kickstarter equipped bikes.    Later this was, per BMW, changed to about 1.5 seconds (UNclear to me, but perhaps this 1.5 was for both...or for the kickstarter equipped bikes...not sure).   The kickstart modules timings were originally longer to allow time to kickstart the bike ....which is a bit strange, since engine rotation supposedly causes the modules to be triggered anyway.  My guess is that the current cutoff was not perfect under all conditions; AND, I think BMW's information was NOT correct for ALL the early modules. The reasoning behind a current cutoff was to reduce heating of the coil(s), which supposedly was THE, or only one of the, causes for the original twin-tower gray coils to fail by cracking.    Apparently, some folks would turn on the key; continue a conversation, without starting the motor.  Perhaps the REAL reason (?) is that some very early modules never had such a timer at all....which I have seen some indication of!  Yes, this is all confused, and BMW's bulletins never helped the confusion, in fact, made it worse.    The coil redesign for reliability (no more cracking) did not result in any change in the electrical characteristics of the coil.   I've never been curious enough to chart all the coil drive characteristics on any of the versions.

Another thing about the earliest modules ....and modules before the final version... was that the module could misfire between the two cylinders.  Weird, but, yes, could happen.   BMW eventually cured this problem in much later modules.  AFAIK, no one has ever reported to the Airheads LIST that they determined this was happening to their bike.  The reason is that is is SUBTLE, and tends to be ignored since it is not continuous for any string of sparks, so might only (MY speculation!) be seen on an oscilloscope ....and maybe the bikes had emissions testing anomalies (a further speculation on my part).  BMW also fixed the modules so that there was NO SPARK unless the engine was being rotated. One could obtain one spark per turning of the KILL switch on and off ....which is handy for certain tests.

Module & coil information IS confusing.  I have re-edited this article; a major goal was to simplify AND increase understanding.   I do not think I have been entirely successful, because I wanted ALL the information here, and there is a LOT of information.  I suggest you read all the following paragraphs on this subject complete your understanding.

Here is information that you may want to at least glance at, for your understanding of the last generations of the electronic ignition used on the Airheads:
If the module has white or pink lettering, it is only to be used with ignition coil 12-13-1-243-910.  This applied to all engines BEFORE 1991.   If the number on the COIL is 12-13-1-244-426, then you NEED the latest upgraded MODULE.   Early & later modules use the same part number!!   The last of these TWO modules
has TURQUOISE lettering. THAT module is usable with ALL the coils, including the last coil, 12-13-1-244-426.  Turquoise, in case you do not know, is a light green, slightly blue-tinged.   Interesting, at least to ME, is that these modules seem to have all been made by Telefunken in Germany, and not by Bosch.

The very last module, usable with all the coils, has the turquoise lettering.   But, it came in two versions:
ONE of these will fit YOUR bike ....because the only difference is the MOUNTING.  A possibly confusing issue is the number, 12.14 - 1 244 477, turquoise, on these late models, so read this entire section, well downwards ....INCLUDING 2. and 3. where information from OAK is located (and MY comments too).

A problem, not so rare, that does NOT apply to earlier models, & NOT to two coil models:
If your bike is hard to start you may have a problem with the early version of the Ignition Control Module, located under the fuel tank.   Versions of these that HAD the problem are coded by paint markings, of PINK ...or WHITE.  The updated module is the above noted 12-14-2-325-284 ...with turquoise paint mark as noted, but some bikes had the other style of mounting, using module 12-14-2-235-550.

If your bike has a hard-starting problem, or single cylinder running until it warms a bit; & you don't want to try $$$ things, such as to install a new pricey module, nor an aftermarket one (which won't have the latest trick changes anyway) can try a NO COST trick.  When your bike is not starting immediately, SHUT OFF the ignition kill switch, then turn it back on immediately; then try starting the bike.   This is not well known, & to my knowledge Oak never wrote about it (?).

Nerdy:There is an interesting way to find out the 'time' for cutting of coil current (assuming it DOES happen, which is possibly questionable on earliest modules), not that it means much to you, actually.    Watch the fairing voltmeter.  If attaching a voltmeter, the indication MAY work more clearly if connected to the ignition switch output, but try the battery first, it is easier to connect a voltmeter there.  You can also get fancy & watch the proper terminal at the module.  From the instant of key-on, the voltage will drop a bit, & may continue to very slowly drop a small amount more. Note the time from the initial small drop TO where the voltmeter gives a SMALL JUMP UP, is quite noticeable. 

Some have used modules from various cars; OR, from Stan at Rocky Point Cycle.  To be safe with coil current, no matter which module might be in the motorcycle, don't leave the key on without starting the engine.  These modules may
or may not handle the latest low primary ohms coils well; and, may not have the various timers & circuitry to eliminate misfiring.  Probably OK for an emergency.

Due to changes made by BMW, & confusion over the issues, I had already begun to greatly expand the above area AND the next LONG area about modules, when I found that Oak had beat me to it!  Well, much of it.  Below I am printing his commentary, as published to the Airheads LIST on May 11, 2011, edited by me for clarity.   I have NOT included the information Oak published in November 2011 AIRMAIL, since I have already covered it in this article in my own way.

Oak posted on December 6, 2003 some of the same information.  I used to have that information in this article, but have dropped most of it, as Oak's May 11th, 2011 & November 2011 information is better.  You also get the benefit of all my own information & interpretations.

From OAK, May 11, 2011, edited for clarity by Snowbum:

1) Here is Oak's May 11, 2011 commentary:
"The ICU (MODULE) version with the heat sink riveted to the ICU is BMW's very latest.  The part number is 12-14-2-325-284. It is now BMW's standard replacement part for ALL models from 1981 forward; has ALL the updates; is applicable for both the kickstart & non-kickstart models. The ICU comes now with the aluminum heat sink attached & is NOT meant to be serviced by removing, cleaning, & installing fresh heat sink paste, as were prior NON-riveted versions."

2) There were SIX prior ICU versions previously used, with the following part numbers; these used a SEPARATE heat sink (that is, the module was not riveted to a heat sink, but bolted/screwed). These types require cleaning & fresh heat sink compound every couple of years. ALL of these are now obsolete, no longer available from BMW.
12-14-1-244-089---Non kick start version circa 1981 thru 1983
12-14-1-244-191-- Kick start version circa 1981-1983
12-14-1-244-226---Kickstart version circa 1983 and later
12-14-1-244-481---12-14-1-244-482, from mid 80's up till about 1987-1988.
12-14-1-244-477---Kickstart & non-kickstart version up till about 1988.  Could replace all previous versions.
Snowbum says:  You will find all those numbers are no longer listed in dealership on-line fiche.  See Snowbum's further remarks, just below:

Snowbum says:
That last one, 12-14-1-244-477, has been seen with the BMW Emblem printed on it; the part was made, and so-identified, by Telefunken of Germany.  The printed part on it is printed on it this way:  12.14-1 244 477, and all the printing is in turquoise.   That is the new module, & you probably will find you have the 0.5 ohm coil, marked  Bosch 0-221-500-203.   Approx 12.4K secondary.  Contrary to any interpretation of the information in the prior paragraph, this module has been seen installed by BMW up to the last of the bikes, made in 1995, and is the NON-riveted construction type.  Typically, you will see this heat sink of the type that fits on the right side of the frame backbone.   NOTE also, that with BMW's change to the one only type of heatsink, there are a few small parts you'd need (see the dealership fiche) to mount the module assembly on bikes that previously had the module mounted on the flat area under the tank ...and I do NOT mean on the right side of the frame backbone. (If you want to demount the module, and mount it on the old area, that's OK with me). I recommend that if you really need a module, you purchase this one, ONLY.

3) There were THREE heat sink design version changes. ALL these heat sinks are obsolete and NOT available.
12-14-1-244-087---First one, in 1981
12-14-1-244-192---For kickstarter ICU's circa 1982/1983
12-14-1-244-328---Post 1983 supposedly for use with kickstart or non-kickstart models.   The casting, rare for BMW, has the actual part on it, and the part is shown this way:     1214 - 1244  328

4).  Why all the changes? There are multiple reasons:

a)  The earliest design, 12-14-1-244-089, provided almost 2 seconds of time for coil current to flow while cranking the engine for starting. If the starter button was not depressed in time, the ICU would shut off the coil current off to prevent spark coil & ICU overheating.    There was a reset time needed which now & then caused starting problems. This created more than enough reason for an update.

b)  There was a kickstarter version 12-14-1-244-191 to delay spark current cutoff for up to 5 seconds to accommodate the slower use for kickstarting.  Replacement choice required care to make sure the correct unit was fitted.  For this version there were some problems.  It was superseded using the 12-14-1-244-226 later design circa 1983 or 1984.

c)  There were other relatively short lived ICU's that followed, without any explanation.

d)  Another problem arose.  Many of the later mid 80's models exhibited difficult starting, frequently firing only on one cylinder. Sometimes it would start easy, sometimes with difficulty. The problem was eventually traced to the failure of the ICU to determine when it should fire for both cylinders all the time always on the power stroke. Sounds strange to the nerdy; BUT,  BMW crudely explained this as a loss of synchronization.  Some users reported needing to place the KILL switch in OFF then back to ON position to re-arm the ignition; then it would start. (see Snowbum's...that's ME...HINT comment earlier in this article).

This problem was followed up with another re-design of the internal electronics of the ICU with a part number change again to 12-14-1-244-477 for both the kickstart & non-kickstart models, obsoleting ALL prior versions of the ICU. Keeping the same part number, it was explained that if a new unit was installed, to make sure it had a turquoise paint color identification to insure the replacement unit contained the redesign. 

What they had done is to re-design the unit so that NO current would flow UNTIL the engine was rotated, such as with the starter or kickstarter. That avoided the overheating problem entirely. 
(Snowbum still wonders why BMW never did this in the first modules). The turquoise painted version was capable of handling the higher current required by a " souped-up" much improved ignition coil, and incorporated the new more reliable sensing of timing pulses, etc.

e)  BMW also had problems with spark coil failure of the earlier single coil from the early 80's onward (Gray coil).  The TWIN black Bosch coils of the 81 thru 84 models are OK and work perfectly. The plastic shell twin tower coils would crack & develop open or shorted windings.  It often showed up as a problem in rainy conditions; but also often in any conditions.   BMW decided to finally fix that problem with an improved coil.  There were two generations of later single coils (with the twin towers).  The first replacement was no longer a gray color.   Some folks used the Oilhead coils, which were not difficult to mount properly. BMW eventually installed the 1991-1995 type coil, often called the Red Coil.  It had a rather low primary resistance, ~0.5 ohm, sometimes measured or described as 0.7 ohm.  The secondary was approximately 12.8K ohms.  These also provided a more powerful spark, with a lowering of primary resistance to permit a higher current. The coil can be retrofitted to earlier models but would require the latest in ICU design due to the higher current need.  It is necessary to use the 477 suffix ICU part number with turquoise paint code, or use the very latest ICU (with the integral riveted heat sink--part 12-14-2-325-284) which obsoletes ALL PRIOR VERSIONS.   BMW warns that you must NOT use the updated coil on ANY of the older ICU's unless the ICU is coded with a turquoise paint dot. If you do use the new high power coil on an incapable older ICU, it will cause overheating of the ICU and very likely cause it to fail eventually.

Oak summarized thusly (again, I have edited this):
There are only TWO module assemblies now available from BMW; 12-14-2-325-284; and 12-14-2-325-550.  The differences are the mounting. The latest ICU with riveted-to-heat-sink construction, for use on the right side of the backbone, should be factory equipped on all Airheads, 1988 & later.   It is fully updated & will handle the new high current hot spark single coil with dual output 12-13-1-244-426.  That coil should be on all 1991 thru 1995 models.   You may need some of the mounting hardware to retrofit the latest ICU & coil, depending on year and model.   The Telefunken 477 is THE module.

Some words of caution involved with use of aftermarket ICU's:     BMW took a long time to get their act together on ICU & coil updates.  Some aftermarket ICU's will work ...or; may not.  They all have the same terminal coding which apparently is standard ...but that is where the similarity may end. The internal designs have been upgraded a number of times.  If you use an aftermarket module,  that is your decision.   The cost savings may be considerable. If it works OK and LASTS;..... you won!

NOTE ALSO, what I have commented on with the modules with turquoise printing ending in 477.

There is often more confusion about the OTHER coils; that is, not mentioned in the previous section.  Some of the literature is wrong ...or misleading.  I also will have a few things to say differently about some of the coils in the long section above!

BMW coil 12-13-1-351-584, is Bosch 0 221 100 022, used on the /5, a points model.
BMW coil 12-13-1-243-452, is Bosch 0 221 101 003, also used on the POINTS MODELS, in the /6 and /7 era.
Both of the above coils have primary windings of about 1.5 ohms each.  It is possible that some literature will say that the coils are the same.  For practical purposes, they do interchange.

Early 6 volt coils (two each are used, primaries in series) secondary windings were ~6.5 to 7 K ohms.  Do not confuse points coils with certain 1981+ bikes that had two 6 volt coils used with electronic ignition; these had primary windings of ~0.67 to 0.77 ohm.  If you used these lower primary resistance coils with points, the points would not last long.

BMW coil 12-13-1-244-142 is Bosch 0 221 100 028.   Some call it the Lightning Bolt coil.   Some literature will refer to 12-13-1-243-142 (note the 243, not 244) as the 1981+ coil with 0. 5 or 0.7 ohms as Bosch number as 0 221 100 313.

The electronic ignition models began with MODEL YEAR 1981.  Because the MODEL year begins in September, some literature might show a -142 coil being used in 1980, or even on R65 models as late as 1982.   Very confusing, & WRONG!  Kind of a nerdy comment here, mostly you can disregard.

Electronic ignition models:   The original troublesome gray colored twin tower single coil tended to crack; fail intermittently; usually eventually totally failing, but initially usually failing when damp.  The Bosch coil 0221500200 was replaced by Bosch 02210500203, BMW 12-13-1-244-426, 1/2 ohm primary, approx 12.4K secondary.  The troublesome coils were also used on the R45, R65, R80GS, R80ST.   The OLD coil was BMW 12-13-1-243-910.  That coil is for pre-1991 engines; control units (Modules) with white or pink lettering are used with it.   The very latest modules can be used with any of the coils!

****Be very cautious about mounting the Bosch "blue" coils ...they can interfere with the fuel tank.

Coils can fail catastrophically, or bit by bit; or, even have a sudden slight failure that remains. IMO, for most failures, it is bit by bit until you seriously notice problems.  Coils CAN act as if 'weaker' if they have an internal wire breakage.  A wire breakage is detectable with a simple ohmmeter test.  Coils with a break in the secondary windings can still seem to work OK ....although may give strange engine power output effects, particularly with large amounts of throttle, which cause higher cylinder pressures and thus more coil power is required to jump the spark plug gap.   The reason that coils can work (maybe); or get weaker with secondary windings having an actual break in the wires, is that the same voltage firing your spark plugs is ALSO jumping across the broken coil wire!  You might never notice, until it gets bad enough.

Coils with an internal short circuit (usually that happens between adjacent turns, or between two close layers of windings) can seem to work OK, but, as with some open's, the spark is weaker; this can show up as what might initially be thought of as a lean-running engine problem ...or, just shows up with large throttle amounts as reduced performance.   In almost every instance, a shorted winding happens on the secondary winding, as just a turn or two problem ...or between two adjacent winding layers. These change the coil electrical resistance value by a really miniscule amount, so is not detectable by using an ohmmeter.  One could compare a good coil versus a bad coil, using the A.C. transformer method or with an oscilloscope, but you are unlikely to have the needed setup ...and knowledge.  Additionally, it might only show up when the coil is under actual stress of operating the engine.  If a coil secondary OPENS & remains open, that certainly IS detectable by an ohmmeter.  Except for weak spark or MANY turns of shorting, or an actual wire being OPEN, there is NO common simple method of coil testing until things get quite bad.

When a coil of any type fails, it often happens little by little.   Coil failures are perhaps 99% more likely on the secondary high voltage winding as such as a wire short circuit or an open circuit due to a broken wire. This will, due to the high voltages involved, slowly (USUALLY) lead to additional such failures, & as they accumulate the coil output DEcreases.

The Airhead coils have a large capacity for our modest to medium high compression 2 cylinder engines that hardly top 7,000 rpm, so some things can deteriorate a LOT before you notice a problem. Depending on the type of failure, you may have poor starting;  this can happen both with a cold engine & a hot engine; you could have very poor ignition at higher rpm (and/or large throttle amounts) ...with stumbling, even backfiring sometimes.

All sorts of failures have been seen numerous times in the various coils ....with a few types of failures specific to certain coil models.  As I noted earlier, the early twin-tower coils were infamous for the gray plastic case cracking.  These coils, sometimes not so nicely called Crack-O-Matics, were first seen on the R80ST and G/S. The case cracking could break wires in the secondary winding, often giving a weak spark, which could continue to deteriorate. The crack could also allow moisture to get inside, completely or almost completely eliminating the spark ....and the coil might not or would not start the bike or it might allow the engine to run very poorly. In some instances, drying the coil THOROUGHLY, & filling the crack with a non-metallic epoxy sealant or glue, could allow a 'wet' tour to continue until the coil could be replaced.  Oilhead coils or coils from another brand were sometimes used as a replacement for the old twin-tower coils.
NOTE!    Contrary to advice by some, it IS possible for two-tower 12 volt coils to fail in such a way that ONE cylinder works pretty well, and the other cylinder misfires or hardly fires at all.  Reversing the coil tower coils will reverse the effect, that is, the cylinders are now reversed in which one is not working properly.   This effect has been seen in failed stock two tower coils as well as failed DYNA coils.  Usually an ohmmeter test either shows an open circuit for the secondary winding, but NOT ALWAYS.  Usually grounding is not the problem.  The best test is a substitute.  If the bad cylinder and good cylinder reverse, it is almost always the coil that is the problem.

GREEN CORROSION in coil towers:

Coil towers (single or dual tower coils, that is, ANY COIL) can get GREEN CORROSION (remove the spark plug wire, look deep inside the tower).  This is usually from small amounts of moisture getting inside the coil tower.  Sometimes it happens from wires not FULLY seated properly, which allows sparking.  Once in a while green corrosion can allow the coil tower internal metal & the spark plug wire metal end to act like a lousy diode & you could have all sorts of effects, including massive radio noise.

Many years ago, power diodes were made from copper oxide coated plates ....same thing was also done with selenium coatings. Besides diode-type vacuum tubes [such as mercury vapor tubes], those coated plates were just about the only diodes available way long ago, and were used with early alternators and in battery chargers, and common in tiny versions in radios. 

Problems can be temperature sensitive. Cleaning the tower internal brass part to clean/shiny will fix the problem.  Do be sure the spark plug wire & end clip all fit properly, and the protective rubber boot is in good condition. You can put a bit of silicone dielectric grease on the wire end clip as you insert it, it will help protect against the atmospheric effects, but industry practice is to NOT allow grease on the electrical ends, but it is OK by me, IF ...IF ...the END FITTING and coil tower inner metal, are both clean and SHINY, and the wire end fitting fits very tightly.  It takes a LOT of pressure to fully-seat the stock good condition brass end fitting that fits over the wire, and goes into a coil tower.  Industry practice is to use silicone grease JUST ON the inside of the rubber cover over the coil towers and where the rubber insert spark plug caps fit onto the spark plug.    I like to have the spark plug wire ends/clip be shiny, the coil tower innards shiny, and I DO use a trace of silicone grease.

Primary windings in coils are usually reliable.  A short circuit will usually not show up on an ohmmeter test; an open circuit will.  Both defects are rare.   Tests are usually done by substitution of a known good coil, as this saves a lot of special testing labor.

Coil towers now and then get carbon-paths, thin black carbon 'lines' that conduct high voltage from the inside of the tower to the outside, and usually extend to the metal case or a terminal.   In a few rare instances the tower rubber boot deteriorates and begins to conduct electricity; almost always viewable in a dark area with the engine running. Carbon paths and/or deteriorated boots are usually easily fixed. Replace the boot, coating the inside of it with a LIGHT coating of silicone grease (dielectric grease).   Clean the carbon path completely; if severe you might have to 'dig into' it, scraping with sharp tools or even using such as dental picks.  Leave NO trace of it remaining.   I usually seal such scratched/etc. areas using clear epoxy or shellac or lacquer or other type of insulating product, even clear epoxy.

All coils were generally quite reliable (excepting the gray bodied twin tower ones) IF NOT ABUSED by open secondary connections.   Once in a while a coil failure is seen. Sometimes from overheating the coil with engine off, ignition on, points closed; other times it is just old age from constant heating and cooling over all the miles and years. 

A not-so-rare problem was seen long ago, when BMW IMproperly crimped the end connectors of the short wire that inter-connects the two single tower coils.  The ignition could be intermittent, in strange ways.  Just fix the wire or replace it. Testing for the problem is easy, use an ohmmeter and pull/wiggle a bit on the wires near the connectors.

Damage to coils is often done by owners, or even some shops, by lifting the spark plug caps off the spark plugs while the ignition is powered. This usually happens during carburetor synchronization.  IT IS A BIG NO-NO to pull off the cap.  The damage, if it occurs, may not show up immediately can suddently show up years later after enough heat/cold cycling.   Damage typically occurs with the engine running ...but damage can happen as the ignition is turned on, caps off. The spark plug caps need to be grounded, via the INternal cap contact and the spark plug.  I will say it again:  Lifting the caps with the engine running for such as carburetor synchronization is a big NO-NO on Airheads.  It was acceptable on the old magneto models, pre-1970, which means BMW bikes before the /5 series, as they had a 'safety gap' structure. BMW erroneously carried over /2 era advice on lifting caps, into the Airheads era & you may see such in some owner's booklets.  DO NOT DO IT!  IMO, It should NEVER be done on ANY engine. You might see such erroneous advice from BMW re-printed, again and again, in such as owners booklets and Clymers and Haynes repair manuals!!

Coil problems can happen from abuse and from old age; as well as to the plastic-cased twin-tower coils from heat/cold cycling.  The earlier gray-bodied models of twin tower coils that cracked are an example. The metal-case coils have the innards potted in tar, and are generally quite reliable.  All coils heat up from both engine heat & primary current flow.  It is possible for coils to overheat on POINTS models.  As much as 70 watts of internal heating is possible in each of the stock 6 volt coils; and, the twin tower coils also can get hot ...but less likely as the electronics modules shut down if the engine is not rotating, and when rotating the current is not steady, as it can be with closed points.  The coil overheating problem happened to the /5 era police (Authorities) models, because they had metal radio frequency covers over the already metal-cased coils ...this keeps more heat inside.  BMW made a change to the dwell angle on the ATU which reduces the AVERAGE value of current DURING ENGINE OPERATION, thus less heat.  BMW did this for all models soon after. It is poor practice to turn on the ignition on points models & forget to start the engine, while you have a 'conversation' with someone. 

In extremely hot weather, with stop & go, such as in congested city traffic, the coils can get stressed from rising engine heat; many cycles of such days can sometimes result in coil failure from such aging.  In less severe use, aging just happens slower.  Heat/cold cycling causes expansion & contraction of the coil innards & eventually can cause wire breakage. The secondary wire size is VERY THIN, a necessity to enable enough turns, so it is susceptible to breaking from coil expansion and contraction.

Coils are not easy to fully test.  Usually an ohmmeter test is reliable, particularly if the coil secondary is OPEN!   All twin-tower coils, even Dyna coils, are suspect.
  A really thorough test means doing the test with the coil both hot and cold.  Coils must produce the electricity to jump the spark plug gap under COMPRESSION PRESSURES, which is far more stressful on the coil than if the spark plug gap is NOT under compression pressure. Coils, mounted in the bike, can be tested for spark appearance (preferably in a dark area) using a very much wider gap than normally used for the spark plug, the plug very securely grounded. The wider gap is a SORT-OF substitute for the lack of compression pressure.  I used to use 'surface gap' plugs, as used on some outboard motors; but normally I just use a modified spark plug, see the photo.  BMW has specifications for spark distance testing; AND, while I do show them later, you should think first, because it is dangerous, & especially because BMW does not specify the shape of the items the spark is to jump from (it is NOT spark plugs for THEM); AND, the tests, if done improperly, which is easy to do wrongly, will injure the coils.   For those interested in modifying one of the ordinary spark plugs from your Airhead, for spark gap tests, simply cut off the GROUNDING electrode, leaving it with sharp edges, but hardly proud of the spark plug body.  If you set this up correctly (ground those spark plug metal bodies!), the use of modified spark plugs is a good test.  If one cylinder is acting up, and the other seems OK or nearly so, SWAP the ignition secondary winding leads; that is, swap the tower leads (on 12 volt twin tower coils), and if the other cylinder now acts, up, replace the coil!

There was actual coil tester equipment in old-time repair shops. These test units were sometimes a combination coil & spark plug tester; but either type was slangly referred-to as 'bomb testers' (yes,really), & used a chamber that could be pressurized by shop air; had a tiny window in the pressure chamber to observe the spark.   However, above the photo I describe spark jumping on a modified spark plug, coil hot and cool, and this IS adequate for testing. 

Use of spark plug adapters that are sold for ignition testing, including for coil testing, such as the Colortune, are absolutely NOT recommended by me (and, for instance, OAK).  They MAY DAMAGE your head threads.  They are NOT useful for testing the ignition system, no matter the manufacturer's claims!

The first updated twin tower coil was black bodied.  

Coil Substitutions, in brief:
An Oilhead coil can be used.  The Oilhead coil was 12-13-1-341-978; the plug housing primary side is 61-13-1-459-515; and the connector for the housing is 61-13-1-459-516.   The Secondary side (ignition cable to the coil) is 12-12-1-289-837, connector for the coil is 12-12-1-705-656 ...needed because the cable can't be screwed into the plug.  Add a rubber cap at the coil.  Bosch does have a part 0 356 250 033-000 plug and it CAN have the cable screwed-in. 

You can use TWO each 6 volt Bosch coils, which can used on electronic module Airhead motorcycles, that is, from 1981. To be really correct, you need the proper coils ...but, just substituting the Oilhead or 6V Bosch coils WILL WORK ...maybe not optimally.  The 6V Bosch coils with the LIGHTNING BOLT on the side has the correct electrical characteristics.  The part number is 12-13-1-244-142.  If substituting for the SINGLE two-tower coil, mount one coil where the original twin-output coil was.  Use that coil for the LEFT spark plug.  Mount the other coil towards the rear, under the relay bracketry, and use it for the RIGHT spark plug.   Interconnect terminals 15 & 1 between the two coils.  The remaining terminal 15 goes to the original green wire; the remaining terminal 1 goes to the remaining black wire.   It is a good idea for the coils to be solidly mounted such that a good electrical contact is made to the metal body.  These Lightning bolt coils are generally HIGHLY reliable, so long as one does not open circuit the spark plug outputs by foolishly lifting the spark plug caps when the ignition is on (this caution applies to all coil ignitions).  You must NOT ground the ignition coil, unless through a 5000 ohm spark plug cap, on electronic ignition bikes.  NEVER, EVER! ....lift the spark plug caps with the ignition turned on!!!

***NOTE: Some models had a reddish colored tower coil from around 1991, and they seem bulletproof.  The red coil has a primary of 0.50 ohm, often said to be 0.70 ohms.  DO NOT USE early modules with these coils .....see information well above & maybe further on.

BTW:  The original gray coil was 1.15 to 1.35 ohms. 

****It is possible that some of the above numbers I use are NOT in the BMW North America ordering system, but they exist ....and your BMW dealer CAN get them.

COILS ...PART 3:    Failure modes, etc.  A simplified, somewhat, version of how coils, points, electronics modules, etc., actually work:

There are several possible failure modes, but the most common CAUSE is that the case plastic (or tar inside of metal case coils) and the copper and iron core parts inside do not expand and contract with heat changes at the same rate.  That stresses the extremely thin wires of thousands of turns, used on the secondary winding.  Being of copper, those wires also expand and contract with temperature.  The wire needs a good compromise in its own characteristics too. 

One or more places in the secondary winding can break, and this can keep happening, over time.  These wire breaks cause high voltage sparks jumping, which further degrade performance.  The main degradation is often short circuits between nearby windings.  That acts, and is, like a single or modest multiple turns shorted loop surrounding the entire coil.  Thus, a double whammy...the open due to the break, and the shorted turn, acting as a shorted secondary winding in itself.   That shorted turn absorbs energy the coil was designed to use to produce the high voltage for igniting the fuel-air mixture inside the cylinder head.  There is a particularly well-known instance, where, on some models, BMW installed a single coil with twin towers (R80ST, R80G/S), the coil case was easily identified because it was all-plastic  & gray in color.  It would test fine when new, but was poorly designed and poorly manufactured. It is tricky to encase the coil electric parts, control the cooling, etc., and the plastic type formulation is critical too............ETC!

Over a period of time these early gray coils had a tendency for the case plastic to visibly CRACK.  The slang-term for these coils was Crack-O-Matic.  The cracking, seen or not, greatly stressed the secondary windings, far more than the primary windings which were usually located inwards, have less diameter, and of much large gauge of wire so less likely to stress-break.  The coil secondary windings opened, sparks jumped across the break(s), ETC....and the coil kept getting worse, until the actual ignition started to fail, and the coil was replaced by a good one.   For the old two-separate-coils models, the coils can fail similarly, but in vastly fewer numbers, and aging failures generally became a very long term event, and was somewhat rare. 

When a single break in a coil secondary winding occurs, the effect "might not be noticed" at all in engine operation at any rpm and any throttle and engine load. As things progress, the coil output lessens more and more, until the engine acts up, the owner complains, and something is done (often, blaming carburetion).    Besides all this, a physically noticeable crack can let in moisture, and many of the coils would fail enough only in rain or high humidity conditions.  The coils might dry out, then seem to operate OK at the next day's start-up.   I have seen these gray coils with quite large and long cracks, as well as some with no visible cracks, which have failed.

Coils heat up not only from engine heat, but also from the electricity passing through the primary winding coil.   I will give an example here of this, as on pre-1981 Airheads, also because there was a specific problem BMW had to deal with, in the /5 era.   The coils are charged from the battery when the POINTS are CLOSED.  The points are closed TWICE, for each points cam rotation.  The period of time the points are closed, with reference to a single 360 degree rotation, is called the DWELL.   The dwell is expressed as degrees compared to a full rotation, and dwell must be large enough for the coil to fully charge for every ignition event to take place properly.  As RPM increases, it is obvious that the TIME for charging DEcreases.  That can LOWER the coil voltage output once the RPM is high enough.  Coils have numerous electrical characteristics, but one important consideration is that the coil output is always to be high enough at any RPM that the engine is likely to be able to attain, and safety factors are added so the ignition will still work well if the battery is not well-charged, a goodly over-RPM factor too.....ETC.

Note:  Points closure is, in effect, duplicated by the ignition control module, in the 1981+ electronics ignition modules.  The dwell angle is different on those models, but all the theory is THE SAME.

When the points close, the coil, having been discharged by the previous spark event, now has ~12 volts applied.  There are complex equations to calculate the coil current at any point of time during the charging period of time, as it is a curved exponential function, and the capacitor, which most think is used only to suppress points erosion from sparking, has a considerable effect.  I will NOT get into any of this, being way beyond what is needed in this posting. 

Simplified for our example here, let us suppose the coil primary winding is ~3 ohms, and the battery is presenting 12.5 volts to the coil, and the points are closed.  Ohms law says that 4.17 amperes is flowing, and the power dissipated in the coil is 52 WATTS.   The ACTUAL heating is LESS, because the points do not STAY closed, and in fact are open for TWO periods during that cam's rotation (2 lobes).  One can calculate by using the DWELL angle; but, the results still are that a considerable amount of heat is developed in the coil windings, and this is besides engine heat rising up to the coil.  The coil can get rather hot inside.  Heating is not good for the coil.  Thus, the coil designer wants low heating, low heat-cold expansion effects, sufficient energy and voltage output, ETC.  MANY MANY decades of ignition coil design experience can still, as we've seen, can result in problems from actual manufacturing practices.  

If the points cam is too sharply pointy, the points may not operate correctly by failure to 'follow' the cam shape.  Compromises must be made for shape....but are rather easily accommodated for modest RPM engines with small numbers of cylinders.   But, the DWELL must not be excessive, or the heat generated in the coil will be excessive.  This happened on the Authorities (Police) bikes in the /5 era.  The basics were the same, but for radio interference reasons, the coils had metal shields around them.  That shield enabled the coils to RETAIN more heat than in the non-authorities models.  Coils began to fail.  The system has always been rather over-designed for Airheads, so BMW elected to change the points cam to one with less DWELL angle.  It worked well, so BMW elected to use the same points cam for all the bikes in the second (of several) points cams era. 

Dwell angle has varied further as time went on and ignition output needs changed, particularly with the 1981+ models that required a more powerful spark to reliably ignite lean mixtures used to help reduce emissions (smog).

There are 'meters' with Dwell function measurements available, usually these are Automotive type Multimeters.  They need not be expensive.  Most do not read properly for two cylinder engines, but one simply applies a factor, and uses the 4 cylinder position of the switch.  Some set points gap by means of a Dwell meter.  This can be quite accurate, but is not needed with our Airheads.  IMO, doing so can even create problems if the points are too narrow from adjustment by dwell angle, and poorly made points can exacerbate the situation. 

The specifics about the ATU's, by BMW and Bosch model number are, of course, shown in this website, for the curious.
More about ignition theory itself, and how the ever-so-simple-appearing Kettering ignition REALLY works, is also on site. 

If you are not completely brain-dead from reading all the previous; is more information; mostly just odds'n ends stuff....before I get into some things in depth!

1. Suppressor (resistor) spark plug caps were metal sheathed from 1970-1976, 1000 (1K) or 1200 ohms nominally, depending on which piece of literature you are looking at.  The tolerance is officially +-20%; so if they measure 800 to 1500 ohms, that's OK.  From 1977 all caps were 'nominal' 5000 ohms.  ALL points bikes can use 1000 or 5000 ohm caps.  NGK caps, with the added rubber protector covers that they usually come, are preferable to the metal-covered BMW/Beru types, strictly for long term protection against spark jumping ...but the BMW/BERU types ARE perfectly OK ....if you clean the insides now and then ...and they do look nice.   The stock electronic ignition bikes (1981+) MUST have 5000 ohm, often just called 5K caps. The 5000 ohms is 'nominal' in specification.   NGK numbers for 1000 ohm caps are LB010F; for 5000 ohm are LB05F.  They make 10,000 ohm caps too (LB10....), so be SURE to ACTUALLY measure them, you MIGHT be confused by the part numbers for 1K and 10K.  BMW uses spark plugs with stud threaded tops.  Get the caps to match!  Some bikes, such as the R65, etc., had metal caps molded to the cable,& most were 5000 ohms.  There is an article on this website with extensive information on spark plugs AND all the NGK caps information, etc.

2. Where so marked, coil terminal 15 & 1 and/or + and -, all have meaning.  With two coils models one coil is jumpered from terminal 1 on one coil to terminal 15 on the other coil.  The remaining terminal 15 goes to the ignition switch; the remaining terminal 1 goes to the points (and tachometer if electronic type) or ignition module.  This maintains proper high voltage polarity at the spark plugs.

There have been instances of misfiring on bikes as shipped from the factory, due to mis-wired coils.  This has been seen only on the R45 & R65 so far as I know.    Example, a 1979 R65:  The REAR coil should have a green/blue wire (12 volt + power) going to terminal 15. On that same REAR coil there is a black/yellow wire going to terminal 1, which connects to the FRONT coil terminal 15.  The FRONT coil should have two black wires going to terminal 15; one is to the POINTS, the other to the tachometer.

3.  QUICKIE TESTING coils & ignition caps:

a. The QUICKEST test is to remove the spark plug cap from both the left & the right cylinder spark plugs.  Insert a longish ohmmeter test lead into one cap, & the other longish test lead into the other cap, both are inserted into the caps at the same time.   You then measure the total resistance of BOTH spark plug caps AND the coil(s). The reading MUST NOT be infinite or in the hundreds of thousands or higher ....that signifies an open coil, open cap, bad wiring, or some-such thing.  The reading should be, with the pre-1977 1000 ohm caps, ~15000 to 20000 ohms.  For 1977 & later, 5000 ohm caps, both points & electronics models, but only for those models with two separate single tower coils, the reading will be ~17000 to ~30000 ohms.  1981 and later must use 5,000 ohm caps.  For those with ONE twin-tower coil, & must-have 5000 ohm caps, the reading will be 22000 to 35000 ohms.  You may find some of these readings somewhat off if you can not tell what the cap resistances are visually, as they are still inserted into the coils for this QUICK test.

1981 & later Airheads have electronic ignition.  The ignition caps absolutely MUST be nominally 5000 ohms each.  DO NOT use resistor spark plugs!!!   Do NOT eliminate the 5000 ohm cap resistors by using a l000 ohm cap, nor, eliminate the cap resistors entirely by using a zero ohms cap.    DO NOT USE RESISTOR SPARK PLUGS.

b.  A somewhat better test (although none of the above, nor this one, nor the following tests, will show up some types of shorts in the coils), is to first unplug the spark plug wires from the coil towers.  Measure one of the spark plug caps with the wire attached to it, from the contact inside the spark plug cap to the  other end of the wire, the folded metal end.  Then measure the other one.  4K to 8K is acceptable for the electronic ignition models; and about 800 ohms to 8K for the points models, although if using zero ohms caps, that is acceptable, although the system will emit RFI and plug gaps will not be as stable, and ignition may, under some circumstances, not be as quite as good.  1K rated caps are the best for points.  The spark plug caps must absolutely not be under 3.5K for electronic ignition models or the ignition CAN BE DAMAGED, over time.   You can also measure a coil tower to any side terminal (single tower coils only);  then measure the other coil similarly.   Be sure the metal at the bottom inside of the tower is clean and shiny. About 4K to 5.5K is OK for either coil.  For the SINGLE twin tower coil, measure BETWEEN THE TWO TOWERS.  About 7.5K to 9K.

The spark plug wires brass pressure contacts SHOULD fit tightly into the coil towers; all need to be clean and shiny, if not, fix that.   I recommend, once things are shiny and clean, that a faint smear of silicone dielectric grease be put on the folded contact that goes into the coil.  Others disagree; industry practice is to use the grease ONLY on the inside of the rubber boot.  I believe industry practice is wrong, because YOU, riiiight? ...will first see to it that your clean/shiny wire folded brass fitting ends fit tightly!...into clean/shiny towers.   If so, the grease will eliminate corrosion .....for MANY years!   Insert the wire, which will need some decent force (I use pliers) to seat it FULLY, it will almost snap into place with enough force.

c.  Measuring the PRIMARY winding side of any coil is more difficult, as for an accurate reading you must short the ohmmeter leads together, then subtract that reading from the primary reading.  The primary reading is low resistance.  Primaries VERY RARELY open or short.  You can simply check for a low resistance.  I won't even list the exact values you might get, but for the twin-tower coil it will be around a half an ohm to around one ohm;  & ~ 1-1.5 ohms for the two coil models.  Obviously the values must not be a direct short, nor open.

d.  The best test
is probably by substitution with a known good coil.

e.   The second best test, & this test is quite good, is that you test a coil both cold & hot with a modified spark plug.   MY method of doing this was described earlier in this article.

f.  NERDY:
BMW published a spark gap test for the 6 volt coils prior to introducing, in 1981, the electronics models.  While I THINK the test is also relatively decent for the electronics models, I have not seen a published test from BMW. The old test is for a minimum 8 mm spark at 300 sparks per minute at 3 volts to the coil; with the spark lengthening to 13.5 mm minimum, at an unspecified primary voltage, at 3600 sparks per minute.  BMW's specification was the same for all the different ATU dwell versions including the early 78 & later 120 with the 1979-1980 points-in-canister model.  You need a special setup to do those tests, which are decently stressful on the coil.  MORE stress than what YOU should do.  You will notice that the test is done at 3 volts of battery power & uses 8 mm AND 13.5 mm test gaps.  13.5 mm is a FAIRLY SEVERE test.  If  you want to make up testing jigs & do these tests, fine by me.   I recommend you don't.  Additional problems with the BMW specs were that the gap test did not, in my literature, specify the two parts needed for the gap, & pointy gaps need less voltage. BMW PROBABLY (?) meant that the tests were to be done with one of their 'tools', & it had a free-air gap, etc.

4.   BMW Airhead points bikes have TWO cam lobes on the Automatic Timing Unit (ATU).  On the models up through the 1978 model year, the points & timing unit are mounted at the nose of the camshaft & NOT in a canister as in all later models.  The forward part of the camshaft, that nose area, of NON-canister models, can be found bent at times. YOU WILL NOT SEE THAT with your eyeball.  There is a way to fix it, with a small brass hammer, but that is not the main point of what I want to say here.  The bent part may be only a fraction of a thousandth of an inch to a few thousandths.  As the ATU rotates, the points will not have the exact same GAP nor timing point ...for both ATU timing lobes.  This will result in a dual-image when using a strobe lamp on the flywheel. The result is vibration, often at one or more narrow ranges of RPM.  This type of problem is often WRONGLY interpreted as carburetors being out of perfect synchronization.    The Dyna dual-pickup electronic ignition will eliminate much/most double-timing, but the camshaft TIP IS fixable.  Another cause for this sort of timing change is advance unit wear &/or irregularity in the grinding of the cam lobes.  BMW at one time actually recommended 'stoning' those lobes to equality.  Don't bother!  But, a quite poor ATU and/or cam tip needs fixing.  The expensive way, DIY, is to purchase a crankshaft triggered ignition.  NOTE that a worn timing chain, chain guides, & wear on one or both timing sprockets, will ALSO cause double images.   Quite noisy chains at on and off idle rpm with the throttle are a giveaway, but the chain need not be noisy.   The "cam tip tapping with a brass hammer fix" must be done carefully, not knocking off the threaded cam tip.  Use of a dial indicator on the smooth side area surface of the cam tip will tell the story....and if you have fixed the problem...or made it worse.   Do NOT try the brass hammer fix unless you KNOW what you are doing, & have a dial indicator, know how to use it, ETC!!

5.   The canister automatic advance had 120 dwell angle for 1979-1980 (points models), and from 1981 (electronics models) the dwell was 104.

6.   The rubber seal strip (or rubber O-ring, whatever you want to call it), located in the PRE-1979 timing chest, in a groove surrounding the points cavity, has two part numbers on the books.  These come in lengths you cut to fit.  Install it after cleaning them with acetone or MEK, & clean the cavity for it quite well too.  Put small droplets of cyano-acrylic glue (CrazyGlue, etc.) in the cavity groove, before installing.   Push a few times into position if need-be, cut with an Xacto knife to fit the ends rather tightly; & let sit overnight.  CLEAN with acetone or MEK again & smear a faint amount of silicone dielectric grease on the surface, before replacing the outer cover. Be careful to engage the outer aluminum cover into the points cavity rubber grommet slot.
11-14-1-265-394 is supposedly 3.2 mm, used until 1974.
11-14-1-262-644 is supposedly 4.2 mm, used after 1974.
If you were to order either, you probably will get just -394 size.  Maybe. You can use a Classic K bike oil filter cover O-ring, which is 11-13-1-460-425, even a used one!  Thanks to Tom Cutter, for that hint.

7.  When working on Airheads, you may occasionally need to know the spacing between markings on the flywheel (or clutch carrier).  You may need to know the distance per degree on the circumference.   The diameter of the larger engine flywheels are all the same; there is 2 mm between each degree.   For the R45/R65, with smaller flywheels, it is 1.5 mm between each degree.

Accel m/c products; 10601 Memphis Ave #12; Cleveland, OH 44144; (216) 688-8303; part of Mr. Gasket group.
Accel points amplifier, wiring schematic:  see page 38 here:
The sketch is for dual plugging coils, but OK for single plug coils.

Technical information on most models is available at:

However, you MAY find SOME of that information confusing I will give you clarifying information here.

For the 70-80 points Airheads, Dyna had an Ignition Booster ....and this can also be used for a dual-spark-plug modified Airhead,  with correct selection of primary coil resistance, to keep within the booster current limitations.  Pay attention to the coil(s) resistance for non-dual-plugged installations too, of course!

Dyna dual-separate pickups electronics ignition design allows separate timing for the two cylinders, which, in some instances, provides a smoother engine.

Many years ago, the original Dyna D35-2 system was NOT a wasted-spark system.  They used DC1-1 green 3 ohm coils on the dual-plugged conversions, the sensor plate had THREE wires.  Each cylinder could be set separately with a timing light.  Since this was NOT a wasted spark setup, each coil fed ONE cylinder (that is, each coil fed the top AND bottom spark plug on ONE particular cylinder).  Dyna has not offered this D35-2 in many years.   Now, what is available is the D35-1, wasted spark model.

The D35-1 has TWO wires at the sensor plate; uses the 1.5 ohm Dyna coils ...which are brown or orangey looking, & are series connected.   Timing is set with an ohmmeter or test light, as you rotate the engine by hand, so watch the magnet location, to know what side sensor you are adjusting.  If using the Dyna TWO wire sensor setup, the two coils will be in series connection for the primary windings. 

Watch out for bad Dyna sensor insulation; that is, broken wires at the sensor plate where they exit the epoxy, & for coils shorting a primary to ground when hot.  Use NGK 1000 ohm spark plug caps.

Dyna sells many different coils. Do not use the Green dual-tower 6 volt coil with the Bosch electronic ignitions that came on the BMW Airheads from 1981.  Those Dyna coils are 3 ohms, and are marginal in that application.

The popular Dyna III model D35-1 was for the 70-78 Bosch coils, or, Dyna coils. 
The wiring for the Dyna box: 
White, left cylinder.
Red, right cylinder.
Black is ground.
The other red goes to +12 at ignition switch & to the left coil (+).
The coils are interconnected by a jumper, same as on original BMW, same numbers at coil primaries, if using those coils.  The right coil (-) is the one with the brown wire from the Dyna box.   Unconfirmed:  Dyna III uses UGS3040T Hall devices. 

The DYNA III, type -1 and type -2 Electronic Ignition Trouble-shooting:
If only one cylinder is working on a -1 Dyna III it probably is a bad sensor. This can be corrosion, so remove the assembly and inspect it; it can be the sensor itself, bad wire, etc.  If both cylinders are NW, it is most likely a bad electronic module, bad coil, or in the wiring.

Disconnect the sensor wires and touch the module end of the input wires to ground.  Do not touch the 12 volt (red) sensor wire to ground.  You should get a spark at the appropriate spark plugs each time the inputs are grounded. If not, it indicates a bad electronic module, a bad coil, or a problem somewhere in the wiring not associated with the sensor plate.  Check the Dyna website to confirm my testing methods!

Dyna coils are color identified (although you can use an ohmmeter):
Blue coil is 0.7 ohms.   Used on 92-95 airheads; secondary is 11.5K.  Includes bracket.  Can be used with any Airhead with the later modules rated be OK for 0.5 or 0.7 ohm primary winding (see much earlier in this article, as this can cover many other years, and yu need to have the proper module).
Gray coil is 2.2 ohms and 14K secondary.
Green coil is 3.0 ohms
Black coil is 5.0 ohms, 17K? 14K?
Brown coil is 1.5 ohms, 14K secondary, for 81-92 stock Airheads, with proper mounting bracket.  Read about the modules!

DC9-1   0.7 ohms;
DC2-1   1.5 ohms.

Alpha (Emerald Island) ignition (canister):
Rick, at Motorrad Elektrik, told me that the brown coils work fine with the Alpha ignition system, the latest version of which works OK with the blue low ohms coil also.   I am speaking here of one single coil, dual output towers, NON-dual-plugged.  I don't know, yet, about using the Alpha2 ignition with the BMW 0.5 ohm coil, limited testing showed OK on my own bike (1995 R100RT), which has BMW's latest module.  See next paragraph:

Ted Porter ( who stocks the Emerald Island electronic ignition (Rick, above, calls his, which is the identical item from Emerald Island, the Alpha 2), has a lot of experience with this ignition, & he reports NO problems with any of the stock coils including 1.5 ohm coils (two in series, 1970-1980 coils), & the later low ohm stock coils, & the Dyna DC9-1 0.7 ohm coils in series, and also the 1.5 ohm DC2-1 single coil.

Boyer-Bransden (aka Boyer):

The old black box Boyer, the Mk3, can be used with or without resistor spark plug caps.

The Microdigital (red box) is sensitive to RF interference, so 5000 ohm spark plug caps are required. The unit won't be injured if you don't use these, but the microprocessor could ...or will ...go crazy and upset the timing.

A URL for troubleshooting the Boyer MK 3: site has a schematic diagram of SOME innards, operation, wiring, & spark curves. 

The early Boyer ignitions have been known to cause rough running problems, & the bike being hard to start.   This is usually from low battery voltage, typically a voltage under 10 or so, and/or SLOW cranking speeds, both of which are disliked by the old Boyer.  The early Boyer models also have an ignition curve that does not match the Airhead engine requirements.  In particular, the early Boyer had an ignition curve that was slow rising & kept rising, there was no practical rising limit ....the ignition would continue to advance with increasing RPM.  Many are in use, however, on Airheads, with no problems 'noticed'.

***I have the schematic diagram of the innards of the old Boyer units (yes, with all parts identified, numbers, etc), & I also have the timing advance curve on the old (& the later, below) Boyer units, & I have it on other ignitions, such as the Lucas "Rita".  For the nerdy, or whomever REALLY needs this sort of information, they can contact me.

Some Boyer-Brandsden's can have a peculiar problem, being not easy to shut off the engine with the ignition or kill switch.  A cure may be available by disconnecting the red fused wire that goes from the Boyer to the battery & the left (+15) coil terminal.  Tape it & do not use it.  Connect both green wires to that coil terminal.

The Boyer-Bransden ignition has been updated.  The Boyer was always an ignition to consider when the tip of the pre-1979 camshaft was broken off, although that IS USUALLY REPAIRABLE.  Now, with the new Boyer model with the updated ignition curve (ALSO available in a modified version for dual-plugging installations) (and supposedly now works OK with a slightly weak battery, low voltage that is, during starting), there is less reason to not recommend it.

Below is the Boyer-Bransden Microdigital Electronic Ignition advance curve, courtesy of
and obtained from Stan Smith when he owned rockypointcycle.
The ignition timing curve shows an ignition advance, a sudden rise in timing at 500 rpm and then a quick drop from ~500 to ~800 RPM, than a moderate rise starting about 1100 RPM. This can cause some noticeable irregularities in response if the engine is idled too slow, even slight strangeness on starting.  Note that this model DOES has a limit on advance, at about 4000 rpm.  As noted well above, the older Boyer did NOT have a limit.

On the chart curve, the ignition advance curve is in crankshaft degrees, the most common descriptive method.  The camshaft degrees method is often called "distributor" timing or distributor degrees.

Other ignition types:

I will add to this section as I get deeper into other types.  Technical information may be put here that is hard to find.  There certainly are ignitions available that are NOT listed here.

Emerald Island (Jeff Lee) canister ignition kit, as sold by Motorrad Elektrik (as Alpha 2) and Ted Porter's Beemshop:    I have been informed by Rick Jones of Motorrad Elektrik that the module on these is OK for driving stock, etc., coils, such as the latest BMW Airhead coils, or a Dyna blue 0.7 ohm primary.  The Dyna brown coil of 1.5 ohms is also supposed to work well, although I personally have some reservations about that one, but have not yet done a full set of tests ...but am running it in my own 1995 R100RT.

Ted Porter (Beemershop) who is stocking the Emerald Island electronic ignition (Rick, above, calls his, which is the identical item from Emerald Island, the Alpha 2), also has a lot of experience with this ignition.   He reports NO problems with any of the stock coils, including 1.5 ohm coils (two in series, 1970-1980 coils), Dyna DC9-1 0.7 ohm in series, & also the 1.5 ohm DC2-1 single coil.  Reportedly the 0.5 ohm BMW coils work fine with it too. I briefly tested that, seems OK.  NO other reports so far.

Crankshaft mounted ignitions:  NONE so far thoroughly tested by me.

Oilheads and classic K bikes:
Information on the module & Hall sensors in the article you are reading has similarities to the Oilheads & K bikes.

Getting deeper into the Airhead (and, much applies to the Classic K bikes) electronic ignition. 
How to Test the Airhead Ignition Module, a more thorough test series.  The more technical aspects, ETC.

Some information & photos below, were from Thunderchild's website, for whom I give credit.  I have done considerable editing & modification to Thunderchild's information, & added my own comments ...mine and his are not clearly identified.

NOTE:  Ignition modules (except riveted models) must have a reasonably fresh thin coating of electronic heat sink paste between the module & the mounting plate.  Failure to clean & re-apply such paste every 2 years or so will cause the module to overheat, interrupting the ignition, & with enough such overheating cycles, eventually the module fails permanently.

The ignition system of a 1981+ BMW motorcycle equipped with electronic ignition consists of three major parts: the coil (or coils), the ignition trigger & automatic advance unit (in a canister) & the ignition control unit called the ignition amplifier or module. The coil(s) are usually easy to test, but verifying whether the trigger or the control unit has failed can be a bit more tricky.  A VERY RARE failure is a coil that fails to work properly when it gets hot.  A not so rare failure is the early ONE coil models, in which the coil is gray-bodied.  Those tend to crack, often visibly, and fail, most often when exposed to high humidity or moisture. A LARGE amount of information on testing various parts is in the earlier sections of this very long article.

In THIS section, I get deeper into technical discussion & testing, with a few repeated things to remind you of SOME earlier remarks.  Following this gray-colored area are more comments, more testing information, etc.

Referring to the wiring diagram, three wires go from the ignition trigger (in the canister) control unit to the ignition control unit (module). The canister Hall device (trigger unit ) obtains power from ICU Module pin 5; the trigger signal is developed in the Hall device and sent to the ICU module pins 3 and 6.   Each time the trigger wire, that is the center terminal of the three-terminal cable of the canister, goes to ground, a spark should be generated from the high voltage produced by the coil(s).

The above sketch has the actual order of pin numbers.  The schematic diagram to the right does NOT show these numbers in actual physical order.

Testing the control unit (module) should be as simple as powering the unit up & repeatedly grounding and un-grounding the trigger wire.   This does not test the module for all conditions of temperature changes.

The procedure is as follows (be sure to read ALL of this!!!):

1) Unplug the connector that connects the harness from the canister to the harness from the control unit. Be careful as there is a small diameter round 'bale' wire used as a clip to hold the connectors together, that MUST be removed first.  For access to this plug, simply disconnect the battery FIRST (to protect the diode board from inadvertently being shorting by cover removal), then remove the metal outer cover over the front of the engine.  The plug is roughly centrally located.

2) Remove one plug from the engine, re-attach the spark plug wire and cap, and fasten the spark plug on the cylinder such that the plug metal body is grounded & you can see the spark gap, preferably in a somewhat darkened area. 
You MUST be sure that the plug is very well NOT just lay it on the cylinder,...rather... clamp or otherwise hold it there... & not with your hand!!!  You can otherwise injure the canister Hall device or the module or YOU, OR BOTH.  I suggest a bungee or sash spring, wrapped around the cylinder and the spark plug metal body.

3) With the connectors still separated, stick a pin or fine wire into the center connector of the 3 conductor white connector coming from engine harness (NOT the canister harness side).

4) Re-connect the battery.  With the ignition switched on, & the bars KILL switch ON,  momentarily ground the pin/wire you just added coming from the center connector. Each time you do this you should get a spark at the spark plug. This will indicate that the control unit (module under the tank) is operational.

5) An even simpler method that can be tried first, but is not 100% foolproof:  Turn on the ignition switch, have the Kill switch in the middle ON position.  Turn the kill switch OFF, then back ON, then OFF.  Every time you turn it OFF from the ON position, you should get a spark.  This tests, as does the previous test, only the coils and SOME of the module, NOT the Hall element in the canister, NOR the part of the module that processes the canister signal.  This test gives different indications if you have the very last of the modules, with the torquoise printing, from Telefunken.

It is not unheard of for the module ...or Hall device in the canister ....or any other piece of electronics for that matter, to operate perfectly when cold & fail when warm/hot.  

Corresponding Ignition Control Unit numbers, compared to Bosch motorcycle standard wiring numbers:

1                    1   coil
2                    31  earth ground.
3                    -   Ignition, - trig
4                   15   Ignition, light sw.
5                    +   Ignition trigger (+)
6                    0   Ignition trigger (0)
7                         tachometer output if used.   Information on the pin-outs, etc., are in SI's as follows:
12-007-83 (2075) of May 1983.   12-006-82 (2061).

In the wiring diagram below, the Ignition Control Unit (Module) pin numbers are NOT in the actual order they are seen on the part (see sketch on the left side for the correct order, which reads RIGHT to LEFT, in orderly progression)...that means that ON THE PART ITSELF, with the unit laying flat in front of you, metal on bottom, pins towards you, the pins are numbered from RIGHT to LEFT, first pin on right is pin #1, last on left is pin #7.  DO NOT!! use an OHMMETER on the module pins.

The sketch is copied from a full wiring diagram. Although not drawn as such in the diagram, the trigger wire (to pin 6 of the unit) is the center connector.  The ignition control unit pin 6 has a brown wire; pin 3 has a blue wire, pin 5 has a green-yellow wire; pin 4 has a green-glue wire, pin 1 has a black wire, pin 2 has a heavier brown wire.

The ignition trigger plug green/yellow (pin 5) may be violet; the blue may be violet/white; and the black may be violet/black.   Inside the canister unit, the sensor has a red wire which connects to the violet or green/yellow; a green wire which connects to the violet/white or blue; and a black wire which connects to the violet/black or black wire the plug.

Testing the Ignition Trigger in the STOCK Canister, all by itself:

DO NOT use ohmmeter functions of your test meter to test the Hall canister device!

The three pin connector that connects the wires from the canister to the bike wiring, as noted above in the gray area, and elsewhere's in this article, has a thin wire bale clip around it that MUST be removed before you try to unplug this connector.  Pry an end, or both, with a tiny tool, & then carefully remove that bale clip.  THEN unplug the connectors. Don't lose the bale wire. Don't spread it too far either.

>>>Many have searched for a replacement for a replacement for a damaged three pin connector.   I have not checked into this myself, but it may be that 90's Audi V6 cars (and others) have one, so you can try a car salvage yard.  Reportedly located in the engine area, left side, near firewall.  BUT: has a brand-new replacement cable assembly parts with plugs, pins, etc.  "BMW R Airhead 3 pin plug set for "Bean Can" Sensor - 12 11 1 244 088-1"

Tom Cutter probably stocks the plugs too.  TPCUTTER@AOL.COM

The ignition canister contains a Hall Effect (magnetically sensitive) sensor; which is a a special type of transistor.  A rotating metal part in close proximity provides means to trigger that transistor. Rotation causes a voltage on the output pin to vary, thereby triggering the input pin of the ignition control unit (module).

Note the diagram showing how to wire
TO  the connector for testing. "To can"  means that end goes to the canister cable plug. The unit is powered from a 9 to 12 volt power supply (just use a 9V battery), & the output from the sensor (center pin) is pulled 'high' (that means positive) through a 10,000 ohm resistor. You read the results on the voltmeter, shown as a circle with V.   As the shaft on the canister is rotated, voltage from the center output pin will fluctuate between a few millivolts and the + supply voltage.

If this makes no sense to you, then it might be wise not to invite trouble.

This will not show up intermittent or heat related faults in the hall device; unless you do temperature testing.

An extremely rare problem is a module that will test OK using the wire grounding method or the Kill switch method, both are in the previous gray area information; AND, this Hall Effect transistor test method with the battery and resistor and voltmeter ALSO checks GOOD.   The answer is a bad module.

Both sides of the connector. Note differences.


Overhauling Ignition canisters:

Some folks who are overhauling/rebuilding canisters:

Overhaulers?    Tom Cutter,   Tom's garage is located in Yardley, PA
Shop:  (215) 321-7944

Dwight Small; 514 E. Grand Ave. #103; Laramie, WY  82070     970-214-2610

He does overhauls??  R-Bike Electronic Canisters, by Pete Serrino

Canister Disassembly, DIY:
I suggest you make notes on what fits where, as you disassemble the canister.

PRELIMINARY (DO NOT START WORK until you read this entire section!):
Some screws may be quite tight.  You need a PROPERLY fitting screwdriver!  Don't bugger-up things!  Remove the pin that holds the coupling to the shaft the end that goes into the camshaft.   You will need a small diameter round drift.   Be careful doing this, some are in very tightly, some are not.  If quite tight, you may want to do this with a press, or make up something so as to use your vise.  Do NOT bugger things up.  Support the shaft!!    You will find some shims and a washer. Remove the cap (Phillips type screws).  That cap normally has a spongy material on the inside.  It tends to deteriorate.  Remove it all.  That spongy material can make a mess inside the canister once it deteriorates it moves all about.   Remove screws for the bearing plate; remove the plate; noting how the plate fits.   Note the big snap ring; how it fits in a groove.  

Remove the C clip.  Remove the three outside screws.  Looking inside the canister, notice the 3 tabs that those 3 flat screws fit into.  Mark a tab & can, so you replace them later in the same position ...(if you want to), but the tabs are not equally spaced, so this is moot.  Now remove the screws.

The flat screws hold the retainer.  That fits the snap ring only in one direction ....a keyhole in the retainer matches a protruding stud on the snap ring.   Note that how the big snap ring fits, where its open end is.

Remove the plastic rivet from the wire strain relief.   Note that the plastic strain relief has a tit, you have to pry or pull it out; once out, the strain relief moves in the slot easily.

The coupler has a spring thing wound around a groove.  Pry an end loose; remove from coupler now need to remove the pin which is now visible.   You need to improvise something that will not injure anything, to remove that pin.  Do that now.

Use a soft hammer to move the shaft through & enable removing the contents, do this a bit at a time with the plastic wire strain relief ...back & forth.  Remove slowly, don't use a lot of force, and write down what you see about about the many washers, etc., you find.

NOTE!   BMW does not sell canister parts.  Motobins in UK sells the springs for the advance weights.

It will be clear to you to remove an E-clip & another snap ring, which hold the shield' in place.   Note the pin, locating the advance & shield.  Don't mess up that shield!  Don't loose the small location pin either.  This is expanded upon in the next paragraph.

Regarding the Sensor (Hall transistor), if yours has failed: Once the canister is basically disassembled, you need to remove the 'vane' without injuring it.  The 'vane' is between TWO C rings.   Remove the top C ring, and remove the pin (very small).  Be careful.  You will have to improvise something for this vane removal.  You can now remove the other C ring, & the 2 flat head screws on the sensor bottom.  The sensor is riveted and you have to drill that out....replace with a steel pop-rivet or nut/screw..  Use a Dremel or similar or?? to grind off the rivet.  See note at end of this canister section, about the dualplate and blind rivet models.   Cut the wires on the old & new sensors, so you can connect them & insulate them (shrink tubing).    Be cautious about the re-riveting; keep things in proper shape.   If the wires are long enough from the sensor, splicing can be done outside the canister.   I prefer them connected inside; the wires kept short enough to avoid fouling on moving parts. The triggering magnet part of the sensor is retained by an E-clip & a snap-ring.  The snap-ring does not hold the rotor in place, the PIN does.  The snap ring keeps the pin in place.   The PIN locates the magnet, with respect to the shaft.  Don't lose that pin. Don't mess up here.   Put the unit over a common socket of correct size, all on your workbench, hit the shaft with a SOFT hammer (plastic?).

It is very important that the parts be very well cleaned, and if need be the shaft burnished in the ATU area.  You need to use some judgment & have some experience here.  Sticky ATU problems show up as increasing idle speed USUALLY when the engine is quite hot; the parts expand from heat.   The weights are on a Teflon thing, don't oil the Teflon unless you have an oil that is exceptionally slow in evaporation & probably contains Teflon; ....I use a LIGHT Teflon grease in that area. 

When doing the final assembly of the canister, pay attention that the shaft continues to rotate freely, in particular as you tighten the side screws.  Ken Lee had one that "dragged the edge of the rotor with the bottom of the sensor housing between sensor and magnet" (his words).  He suggested cutting a small relief slot with a Dremel tool for clearance.  When mounting the canister to the engine, install a new O-ring at the base.

The sensors vary somewhat in how they look or are mounted. Pay attention to what you are doing.  The canisters that have a lower plate & upper plate assembly with the blind area can be worked on with some thought.   You could drill a couple of access holes for a riveting tool.   The Classic K bikes use two of the same type of sensors, just not in a canister!  Oilheads are similar.

Below is a link to George Turski's photo-show on flickr, on cleaning & lubricating a canister ignition.  I caution you to pay attention to my comments here:
1. Write down exact descriptions of where & how various washers, spacers, etc., are mounted/located.
2. Do NOT deform the advance springs by extending them AT ALL beyond their normal stretch.  You can see how much that is, by moving the advance weights to their stops. Do NOT remove them at all if you do not have to.  If springs are already stretched, & weights would not be always fully returned at ZERO rpm, then replace the springs.  Motobins, in U.K.
3. Don't lubricate too much. Use very light grease or a medium oil of long life quality.
4. BURNISHING (metal polishing) may be needed.  I use super-fine-grit silicon carbide paper & kerosene.

A group of photos on how to clean and lubricate the ATU (by George Turski):
This link is provided by me here to give you an idea of what things look like, and is not how I personally would necessarily suggest you do a cleaning/lubrication/repair/etc.

Another do-it-yourself, cleaning and lubrication of the ATU:

It appears that there is more than one style of plates/sensor items.  The mounting plate may have a second plate affixed; then you can't drill one rivet & use screws and nuts.   One rivet can be ground down from the top plate.   The new sensor comes with the mounting rivets imbedded in the plastic housing.  You won't likely find a way to flatten the blind rivet BETWEEN the plates.  You can remove those rivets, & use the holes for your own rivets.   Make sure the sensor is flat & flush with the plate is a bit tricky, clearance is tight for the rivet tool, although you can modify one.

If you are modifying the canister ignition timing limits stops in any way, see the next section.

Modifying the stock canister for dual-plug conversions:
This is, or is not necessary, depending on who you talk to.
See the previous section(s) for comments about opening the canister.

One Popular Point Of View, which I shall call PPOV-1 here, is to use an IDLE ignition timing of OT, or very slight advance from OT; & leave the canister advance unit stock.   It may be recommended you bend the advance ears outward just shy of touching the canister case inside wall.  That adds a small amount of maximum advance.  I personally have done these things & also sometimes just opened the canister and modified the weights/stops for additional advance. NEITHER is a must.   It is a fair amount of work to take a canister apart to modify the weights & stops. I have never published the exact method & amounts of grinding, etc. Bending the advance ears as noted, is not difficult, & you need only remove the tiny oval side cover to do it.  There is one additional item I should mention.  Using this sort of OT timing (idle rpm) will result, during carburetor synchronization, that the carburetor butterflies are being closed a very tiny bit more than stock (reasons in my carb articles). THAT also happens with ANY dual-plugging! Thus, there could be (NOT always is) a SLIGHT stumble as you GENTLY open the throttle from the idle position, usually, if ever, noticeable at takeoffs from a stop.   The cure, for complex reasons, is to INcrease the size of the IDLE JET ...a typical increase would be stock 45 to 50 or 52 or 55.   NOTE that this effect COULD ALSO be seen in using the S mark timing, PPOV-2, as in the next paragraph.  Note also, that the effect has been seen, AFAIK, only with Bing CV carburetors.

PPOV-2 is that the stock S mark advance should be used ...AND, the advance should have its total amount available shortened a bit.  The typical reason given is that dual-plugging does amount to an advance of timing, in itself.  That is true.  That is compensated for, in POV-1, by retarding the idles spark adjustment from S to OT. 

For PPOV-2, an interesting article was posted by Pete Serrino. He recommended using one or more layers of common electronics shrink tubing over the advance weight stops.   He did not specify the exact type of tubing, but said that one layer of tubing shortened the curve by 2 crankshaft.  Snowbum notes here that 2 is NOT as much as the difference between S and OT, which varies by model/year, but is either 6 or 9.  Pete uses 2 layers for dual-plugged 336 camshaft bikes, & 3 or 4 layers for 1000 cc 308 camshaft bikes; & one layer less on 800 cc bikes.   I do not think that restricting the advance range is absolutely necessary for this S timing method.  I think it depends on many factors, including the compression ratio in use.   Pete also said that drilling the weights with a 1/4" hole about 2/3 up from the pivot point & a 1/8" hole close to the first hole, will move the rpm up 500.   I have generally preferred slightly stronger springs to slow the advance (increase the rpm at which maximum advance occurs), but, like Pete, I never found many springs that did it, although some Porsche ignition springs were quite good enough. I have NO problem if anyone wants to modify the weights.

I have also modified the weights ON STOCK, SINGLE PLUG ENGINES, to set the maximum advance at about 3500 RPM, which allows a bit more compression ratio on Regular grade fuel ...or, allows a somewhat higher CR with higher grades.

I have purposely not expanded this section on these modifications.
I have an article on dual-plugging:

Addendum, miscl. notes, wrap-up, etc.:

1.  K bikes, and many other bikes, do not have timing marks on flywheels, etc., for setting the ignition timing.  In some instances, the ignition timing is set using a factory tool of some sort.  Often, the ignition is specified to 'fire' at some specific distance of piston travel, almost always a certain distance from TDC.  Occasionally in degrees.  Article 72, formulas, includes the method for you to do the calculations, plus, a link to a website article that automatically does it for you!

2.  A RARE, but super-annoying problem, because you likely will go CRAZY before you find the answer, is a 1981 & later electronic ignition Airhead, that typically will idle OK, but won't raise rpm up properly.    This problem acts somewhat similarly to a hole in the carburetor diaphragms.   The actual problem may be a poor ignition kill switch at the bars.   Cleaning that switch may not fix the problem.  Bypassing the switch will show whether or not the problem is that switch.

09/16/2002:  Wire color code, notes, links fixed and verified; red emphasis areas. Additional changes to clarify meanings.
01/25/2003 to 02/05/2003:  Clarifications, cautions, add Newark part for Hall element; canister/high idle note; clarifications & grammar & minor typos.  Points parts number; gray coil information; information on Dyna & Boyer module timing & color coding information; rearranging & editing of little consequence; other modules from cars; add suppressors information; info on dwell; canister shaft swelling; Bosch module versus SYSTEM, which I've colored, just above the sketch, as green.
05/15/2003:  Minor clarifications, more information on coils; fix hyperlinks operation.
05/15/2003:  Correct .htm, I upper case must be i lower case.
07/13/2003:  Hyperlink for #2.
12/05/2003:  Greatly expand information on substitute modules.
02/03/2004:  Expand on modules and coils slightly in preparation for information to be obtained in future.
03/09/2004:  Update slightly, not uploaded.
10/31/2004:  Add several URL's; edited entire article for better clarity.
12/30/2004:  Expand information on alternate sources for canister points.
04/09/2005:  Add note at very top.
05/11/2005:  Oak's info from Airlist re Electronic module & coils; + slight revision here & there due to that.
03/22/2006:  Add Stan Smith, Rocky Point cycle as source, and Transpo number.
04/13/2006:  Correct hyperlink to ...oldbritts....
05/30/2006:  Updated things on the new modules and coils, for clarity.
11/16/2006:  Minor editing & updating/expanding information on RockyPointCycle.
11/23/2006:  Add another source for the Hall elements.
11/27/2007:  Technical details updating.  Modify testing & wiring notes.  Stopped major updating, awaiting when I can personally overhaul a canister, step-by-step, making sure that section of this article is clear to anyone.
01/12/2009:  Add Boyer curve; change my recommendations & feelings about it.  Fixed some typos, expanded some things to improve clarity.
02/05/2009:  Update Dwight Small's information.
02/08/2009:  Remove a few spaces, add note about being only 1/3rd way down the page.
04/30/2009:  Minor correction (clarifications really) to ICU pin functions.
11/12/2009:  Minor updates; primarily was removing outdated links, and do some clarifying.
01/01/2010:  Expand, slightly, points amplifier section.
02/16/2011:  Information on faulty 1970-1978 points.
03/01/2011:  clarify information on hard starting module problems.
05/06/2011:  Add note regarding motorcycle module locations and which are to be re-coated, which not.
05/11/2011:  Revise article for clarity, eliminating duplications, expanding commentary on the coils and modules, clarifying many issues.
05/15/2011:  Add one troubleshooting link to Dyna information.
06/07/2011:  Add + - symbols to the test with connector & voltmeter & 10K resistor sketch.  Add more information on how to test for ATU problem with high idle rpm.
07/29/2011:  Clarifications in NOTES section.
08/29/2011:  Add note about 3 pin connector being available at car salvage yards.
09/21/2011:  Correct Dwight Small's information; re-arrange where aftermarket rebuilders are listed.
11/06/2011:  Minor clarifications on modules.
01/11/2012:  Add a bit more to the old points commentary.
03/20/2012:  Add this section: How to test for a bad Hall element in the canister.
07/05/2012:  Remove link to BMWScotters article, link is dead, and info can't be found from a site search.
07/17/2012:  Add links to Wade's information and as source for HES units.
07/26/2012:  Add more information on ATU and cam tip problems.
10/30/2012:  Re-arrange #9 & #10 & greatly expand information on coils & caps resistance values.
02/14/2013:  Again, expand information, mostly on coils, and at same time CLARIFY details for understanding by any reader.
04/30/2013:  Add this to article 2 plcs:  that Tom is quite slow in shipping the Hall elements he has for sale.
05/09/2013:  Add a hyperlink, Boyer versus Lucas-Rita.
05/12/2013:  Remove Dyna troubleshooting link, add information on troubleshooting.
07/22/2013:  Add section on timing lights, prompted by similar article I wrote on the Airheads LIST.
09/21/2013:  Add #11.
09/24/2013:  Fix typo on points description (1979 should be 1978) & add notes on BMW part numbers for points for NON-canister.
10/20/2013:  NOTE:  The bmwscotter website appears down for non-payment of ISP fees.  Added that note to the DYNA section.
12/06/2013:  Start an Addendum/notes section
02/14/2014:  Editing for clarity in a number of places; added links & information that I have schematic, etc., for higher amperage points booster/amp.  Add 9.e.
08/23/2014:  Clean up article some, compressing size for enhanced display on small devices. Change name of link to the Boyer ignition curve, to avoid problems when presented in an internet link.
08/28/2014:  More editing, and again on 09/17/2014.
10/14/2014:  Re-write the High Idle RPM section.
10/15/2014:  Add link and comments, re: George Turski's photos of canister teardown.
10/23/2014:  Fix improper link to my single plug article.  Re-arrange entire article, fix typos, etc.
11/22/2014:  Split 5 into 5A and add 5B section.
02/25/2015:  Add emphasis, in red, to the Bosch coil number ending -200.
05/06/2015:  Add addendum item #2.
05/30/2015:  Minor changes to Dyna area, and add comment there.
09/08/2015:  Start section for 'other' ignitions, and a bit of updating on 09/11/2015.
12/28/2015:  FINISH MAJOR revision started several days ago. Remove numerous bad links. Clean things up.  Increase font size.  Fix colors. Fix left justification, update meta-codes.  Addition information on rare kill switch problem. HUGE repositioning of items. Expansion of information in many places. SIMPLIFY & condense for clarity.
02/17/2016:  Update information for Dwight Small; delete source for canister overhauls by Motorrad Elektrik.
03/05/2016:  Meta-codes, left justification, narrowing.
05/10/2016:  Add commentary about the -477 module, and noting that things are still a bit confused.
07/03/2016:  Remove link in the Addendum, regarding GM HEI module use with points. H.L. to 100%.  Eliminate one redundant script.
07/23/2016:  Minor updating of metacodes, scripts, H.L.   Updated explanations. Add photo of modified spark plug.  Major updating of layout.
07/30/2016:  Update availability of canister repair kits from Motobins, Euromotoelectrics, BMW.
10/21/2016:  Add George Turski's photos on canister ATU overhaul, via his hyperlink.
11/30/2016:  Add references to Accel amps.
01/09/2017:  Re-work all HTML so that colors, fonts, layout, horizontal lines, etc., are standard numbers and display properly. Improve clarity here and there.  Reposition some text.
01/21/2017:  Clarify and correct the description of coil terminal numbers and wire colors, for the two coil models, and, specifically, the example, a 1979 R65.
03/05/2017:  Fix sparkplugs hyperlink in table at top of article.  Fix minor HTML problem in revisions area.
05/17/2017:  Add Section 3 about coils, points, module, failure modes, etc.
05/19/2017:  Fix Section 3 to reflect true max DC current, and add note about dwell reducing the current.
08/11/2017:  Minor updates on sources for overhauling canisters.
09/28/2017:  Expand, slightly, information testing coils and what to expect if a problem.

Copyright, 2014, R. Fleischer

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Last check/edit: Friday, November 03, 2017