CV Carburetors, overhaul, etc., Part 1 of 2 parts
basic mini-overhaul can be done with the carburetors in
place on the engine.
READ Article #6 on the R75/5
carbs....some really IS pertinent to all the CV carbs:
READ: http://bmwmotorcycletech.info/bingcv-2.htm That is Part 2 of the article you are reading now.
Below is a website in which you can enter your carburetor
model number, and get a chart showing all the component
NOTE: The float needle tips
tend to get faint grooves in them after a lot of miles, and, if a rubber-tipped type,
the tip "rubber" material gets slightly harder, and (modern gasohol especially)
deteriorates them, and then the needle
tip does not seal well, causing the bowl to overflow onto
your foot. This can also happen if a TEENY particle
of dirt gets into that float tip and mating seat area, and
also if the float deteriorates enough. The
stock float and float needle probably should be replaced
every 30,000 miles. It is VERY common to see a carburetor overflowing onto your boot. Most Airhead owners have had the problem at one time or another. The fast fix is to turn off the fuel petcock(s), remove a bowl, and jiggle the float up and down with the fuel ON, to flush out any particulate matter in the float needle-seat area. It is important to keep the fuel tank clean, and as they age, the interior reddish-brown lining deteriorates, clogs screens, etc. Use of aftermarket fuel filter(s) below the petcocks is almost a necessity now, with the aging bikes. Information on screens, filters, updates, etc., is elsewhere's on this website.
NOTE: Except for the earliest carburetors with no plunger on the float needle (no rubber tip on the needle either), if you left the teeny clip off the float needle and float, the chances are that the float system will work just as it is supposed to. You COULD, however, have a situation where the needle ‘stuck’ to the needle seat, and no gas flowed. FYI, I used to purchase these wire clips about a dozen at a time, and I used to need one every few months when I had the shop. It is ever so easy to have one flip someplace while trying to install or remove. I used a 3 power magnifier on my eyeglasses, and always did the work on a piece of old white bed sheet! I tried magnets, some help, sometimes not.
On the EARLIEST carbs, the needle was all-metal. Bing had some problems and made several changes, approximately at the same time. The needle was changed to some sort of rubber-tipped type; the needle lower end was drilled, the needle got an internal spring loaded-plunger with a teeny hole at the bottom end, on the side, and the clip was installed. I believe that Bing incorporated the spring loaded plunger so that the fuel level sensing was more accurate, and so the needle would wear LESS, as less pressure was needed to close the orifice off, but more was available. That is, the LEVERAGE is such that as the fuel level rises, the pressure on the seat increases rapidly, compared to a very small fuel level increase. This is difficult to see, and a nerdy point anyway.
I believe that as the plunger tip wears, which it does and the wear shows as a ring, the needle, being loose-enough in the vertical well area it fits up into, could cant sideways a bit. That MIGHT allow the grooved fuel shutoff needle to hang-up ever so slightly in the SEAT. Since only the needle weight, plus weight of fuel, and maybe vibration, etc., is going to be moving the needle downwards to let fuel in, Bing incorporated the clip, so as the float assembly went down as fuel level dropped, the float assembly positively pulled the needle off the seat.
NOTE: Replacement of a float needle SEAT is rarely needed. Detailed information is here: http://bmwmotorcycletech.info/bingcv-2.htm
FIRST section: the floats, my testing, information on failures, alcohol in fuels, etc.
The reason for the floats failing even when they weigh less is not well understood. It SEEMS to be a shift in mass, and the outside dimensions do NOT hardly change. Remember that this does not always happen, and the floats mostly fail by increasing their weight. The floating test is the only good test.
Information from extensive testing on a large number of floats was FINALLY! completed, after some months, on July 13th, 2003. I had accumulated a goodly quantity of used Bing plastic 'one-piece-assembly' floats, for which I hereby give special thanks to all those who sent them to me. These floats came from both slide and CV Bing carburetors, some were very old indeed, and others not very old at all. Testing took months. Since the floats were WELL dried out when I received them (At first I hardly understood a problem THAT brought about), I had to take measurements of various sorts and then put them in sealed glass containers with various fluids, and let them soak at least a month, and then retake many measurements. Weight was a primary concern, but I was also interested in mass, distribution of the weight/mass, dimensional changes, etc.
There were some surprises. I had
EXPECTED to find that some solvents would actually start
visibly destroying the floats, but this did NOT happen. All
sorts of liquid solvents were used, many of
which were known ingredients in gasoline's from across the
country. I obtained samples of gasoline free of alcohols,
free of MTBE, free of ETBE....etc....as well as gasoline's
WITH those additives. I did testing of the floats in
specific liquids/chemicals. I also did some testing by
MIXING various chemicals/solvents, as just putting floats
into a single solvent is not, theoretically, adequate to
establish all possibilities.
I hardly think I exhausted all the
There are THREE common types of
alcohol, isopropyl (rubbing alcohol), ethanol (drinking or
corn) and methanol (sometimes called wood alcohol since
that was one way of making it, nowadays it is made from
natural gas; and, it is very poisonous and quite
corrosive). Generally speaking, methanol can cause
corrosion of aluminum, can be hard on rubber and plastic
parts...and brass parts. THAT covers just about everything
in your airhead's carburetors but the steel pin, needle
and the diaphragm, and those can be affected with water in
the mix. Other additives are not great either: ketones,
ethers, etc. Common 'gasohol' has 10% alcohol, but may
contain LOTS of other 'things'. The alcohol in gasohol
will raise the octane, but leans the mixture in the bike, which is why
most FI cars can get away with using it (at a cost in
mileage and some in power), but many older carbureted
vehicles will not like it. The better of the alcohols
is isopropyl, it tends not to separate out, and is fairly
stable. Isopropyl, however, is not the alcohol of choice of
the vested interests that grow or sell corn or the
politicians who have, well, interests in this area.
It is hard to give solid recommendations on storage of
today's gasoline's. Generally, with the use of
a product like Stabil, a few months is the best one can
hope for. It is better to clean and then dry out
the system, including the tank. In fact, cleaning
the fuel tank thoroughly should already be on your
A product often called 'dry gas' is sold to car owners in
wintry States, as it, an alcohol...usually methanol or
isopropyl, mixes with water at the bottom of the tank, and
in fuel lines, enabling the water to be 'burned' ...so to
speak. Adding that product MIGHT increase the alcohol and
water content of the gasoline to a critical level...causing a separation process...and water and
alcohol will now be at the bottom of the tank, rotting out
the tank....or, worse with a premix two-stroke
engine, the oil could separate out, and the engine would
not get lubricated.
***I should note here that some folks
sent me information on weights that I could not duplicate.
I was rather suspicious, and then I made an interesting
discovery. If a float was never dried out thoroughly from
first being put into service, UNTIL removed and replaced, and
then sent to me, then the weights might tend more to agree
with information I was given, as those weights were taken
right after removal. My conclusion was that it
is likely that the first (since brand new) and constant
immersion in fuel changes the float in weight/mass movement
vastly more on a percentage
basis, than after the float is dried out from some years of
being in service, and re-placed into gasoline.
This might show up as a smaller effect if my testing had
gone on for MANY months in the various liquids.
MIGHT. I was a bit intrigued by this
idea. I did some experimenting with cutting open and
drying, a few float assemblies, but NOT loosing any of the
material...and it appears that my hypothesis may well be
correct. While someone could compensate their floats
for this effect (by measuring actual depth in the float
bowl and adjusting for that....AFTER drying the floats
really well after long usage....it is a moot point, as I do
not really recommend this. Saying this
all a bit differently: it APPEARS that a brand new
float, once put into gasoline and kept in gasoline (except
perhaps for very short periods allowable without
gasoline...such as carb bowls off, perhaps for a day's
overhaul), changes internally, and that internal change is
permanent...or if not, it takes a VERY long time for the
change to revert any.
Follow-up: I managed to obtain a float and do some retesting during the late Summer and Autumn, of 2005. This time, I measured only weight, and the only liquids being tested with the floats, after a couple weeks of soaking, were hi proof ethanol; anhydrous methanol; and a refinery product of mixed solvents/items, that I obtained from a refinery worker....this type of mixed solvent is a byproduct, generally, and is often mixed into batches of motor fuels, to get rid of it...and for?? reasons. Also, in this particular series of tests, only the SAME float assembly was used, thereby exposing it to a series of solvents. The float assembly started out as 197.2 grains, and no matter what solvent, nor at what period of time, the weight never exceeded 210 grains. I was able to obtain some other exotic solvents, and did some brief testing on them. Same results, tad worse.
Bottom line: I am almost certain that the problem with the one-piece float assembly is one of very long term exposure to a mixture of various solvents in common gasoline's, and that those gasoline's that have, perhaps, alcohol and/or MTBE, or similar, will be affected MORE.
I do NOT recommend Bing so-called
alcohol-proof float kits (dual independent
floats). HOWEVER...if you are willing to fiddle with
these, and understand the limitations, then their use is OK
with me. There are several reasons. Bing said,
years ago, that they would give increased mileage and
performance due to stability of the fuel level during
turns. I agree, but mostly only in an airplane or with serious
racetrack use where the bike is leaned to extreme angles. These independent floats were originally advertised as
being for engines where the carburetors were facing more
left and right than on our Airheads...more or less fore and
aft. One must think about the way the floats
are hinged and operate, and then one will see that Bing's
old claims for our bikes were hardly reality.
As to their NOT being affected by 'alcohol'....that may be
true. For EITHER
the stock OR Independent kits, you MUST replace the float
NEEDLE regularly....as it is the SAME needle, for BOTH.
These kits were originally sold with plastic bowls. Those bowls have been known to develop cracks, often microscopic, that cause weeping of gasoline. The latest Bing bowls are zinc metal, like the original stock bowls. They are EXPENSIVE, and NOT available from BMW (BMW carb parts prices are often MUCH cheaper than Bing's!!).
****NOTE: The old method of turning the carburetor upside down for adjusting the float level is no longer used for the STOCK one piece white floats...but it IS for these Bing dual independent floats! At least per Bing's sheets. However, by using one's finger, carefully, one can adjust the float bridge of these Bing kits, whilst on the bike...and Bing's latest sheets reflect both methods of adjustment.
independent float conversions, here are some adjustment
To adjust whilst on
the bike, maintain the arms parallelness to each other, and
adjust for 0.412" from the arm lower edge to the
carburetor body, at the point your finger VERY LIGHTLY
pressing on the arm assembly, causes the float needle
plunger tip to NOT QUITE start moving upwards.
Once in awhile deposits of fuel residues will get into the needle spring and cause it to malfunction. The float needle tip also wears out. Thus, the float needle should be replaced at regular intervals, just like the stock one, and they ARE the same part....as delivered from BMW or Bing. I recommend 30,000 miles. It appears that the floats will NOT require replacing on the Bing KITS. I'll say it again: The float needle is the SAME as on the stock carburetors, so it is available,...from your BMW dealership. GENERALLY, stock Airhead Bing parts are CHEAPER from the BMW dealership, than directly from Bing.
****That clip is not used on the models 64/32/1-20****
The float needle lower end may have a tiny hole in it, that the wire clip fastens to, and this end part rotates easily.... some may find it a more than a little bit of an annoyance reassembling these. When installing the float, float pin, float needle and that tiny wire clip, they must be installed as an assembly, a bit tricky, especially if the carburetor is right side up, but doable. I suggest a white sheet under the carbs, in case you 'loose' that wire clip or needle. I highly recommend that you order SEVERAL of these wire clips when you order floats and float needles, as they are SO easy to lose. ALWAYS replace the float needles when replacing the stock float and vice-versa. When the float needle tip gets bad, the carburetor will leak on your foot, the mixture gets very rich, and the mileage goes way down.
***A very rare problem is a float
needle that seats irregularly, yet a new needle,
sometimes someone even replaces the needle seat, does not
fix the leaking. INSPECT the float tang...it
needs to be flat and NO irregularities in its approximate
center where it contact the bottom of the float needle.
This is very rare since most people have to replace
floats long before this wear is noticeable.
BMW dealers prices are generally
CHEAPER than Bing prices.....and you can NOT depend on
Bing USA parts being of the same quality as the BMW sold
parts. Be careful! .....and do NOT use
The very earliest /5 diaphragms
were replaced by a thicker type, which is all that is
available now. Some of those very early ones might
still be around.
NOTE: Do NOT!!!...NOT!!!!...use anything but BMW Dealership or Bing Agency furnished BMW diaphragms! You may run across articles that say that you can substitute Zenith Stromberg diaphragms, used on some Volvo's, ETC., for certain Bing diaphragms. You also may find that if you do this, they may work OK, BUT MAY work marginally. There are differences, in material/thickness that do NOT seem consistent. The Stromberg CD150 diaphragm does physically fit the 32 mm Bing CV; and the CD175 does physically fit the 40 mm Bing CV. DO NOT USE THESE.
With some Airhead carburetors BMW does not offer just the diaphragm, and wants you to purchase the slide with the diaphragm attached. This may occur with the models where the diaphragm is attached by a pressed-on nylon ring. If you want to, you can purchase the diaphragm from BINGUSA. You CAN pry the ring off without breaking it ....if you USE VERY HOT WATER, EVEN BOILING WATER, to soften and expand the ring. Be gentle, do not try to open the ring too far.
I recommend you do NOT get carburetor rubber parts from BINGUSA; get them only from a BMW dealership, they will be correct color and type of rubber, etc. It would be better if you obtained the diaphragms from BMW dealerships too. BMW dealers prices are generally CHEAPER than Bing prices.....and you can NOT depend on Bing USA parts being of the same quality as the BMW sold parts. Be careful! .....and do NOT use Stromberg diaphragms!
Diaphragms may have a downward facing tab that fits into a small recess in the slide itself. Diaphragms have a somewhat larger downward facing tab that fits in a corresponding slot in the top of the main carburetor body. Tabs and slots must line up during the actual fitting of the parts, and it is easy to accidentally rotate the diaphragm when putting the carburetor top back on. When assembling the diaphragms to the slides, be careful that you assemble things concentrically and carefully. If the needles are still in place, be extra careful not to bend them!!! Tighten the top of the carburetor screws evenly, coat the threads and underside with a WEE tab of antiseize, and do NOT overtighten..
With the central jets parts assembled, some care and wiggling may be necessary to install the slide and needle assembly in order to get the needle into the lower brass tube area. NOTE that many have initially assembled the atomizer jet wrongly. In the Bing CV carb, that atomizer must stick UP INTO THE CARBURETOR THROAT. If you assemble wrongly and then put a wrench and some force onto the central jet assembly, you can destroy your carburetor.
The central jet assembly top-most piece is a tubular brass part with some holes (this item is called an atomizer). This loose part (as you begin reassembly) fits directly above the tubular part called the needle. This atomizer must stick up INTO the carburetor throat, and only ONE end of it has the correct diameter to allow it to fit up into the throat. A problem can come about if one has the slide, diaphragm, and its wiggly needle already in place in the carburetor, and you now try to install the central jet assembly. First, be sure that the black rubber O-ring on the central jet assembly is in good condition,... if questionable, replace it, and use a wee bit of silicon grease to help its installation, AND on the outside of the O-ring (I also place a WEE bit on the threads of the jet assembly) so the jet screws upwards easier. Regarding the mentioned potential problem: When installing the atomizer, ETC....be VERY careful that that the proper end fits into the throat, and that the needle does not catch the edge of the jet....you might not notice, and then screw the jet upwards, bending the needle...or worse yet, applying too much force and breaking the threaded carburetor boss. NO excessive force is needed here!!! SO, if the slide with its needle is already in the carburetor, be especially careful installing the central jet assembly.
Slides are reinstalled into the carburetor clean and dry, and the lower jet assemblies that the slide needle fits down into, really should, ideally, ALREADY be in the carburetor!! If you are careful, see above paragraphs, you will be OK.
When assembled correctly,
the slide, which has two holes at the bottom, off center,
will have those two holes facing the cylinder
head. Slides work OK even when fairly well
worn. Bing has been offering some slides
with O-rings. They are quieter, in a few instances of
Sometimes the brass atomizer part
that sticks upwards into the carburetor throat does not
fall downwards and out when the central jet assembly is
removed, or does it later when you are not looking!
Use a toothpick or similar to gently dislodge
it. It is easy to lose these parts, so do
NOT! Remember, I recommended an old piece of
white sheet under the carburetor if on the bike. Once in
awhile, that brass atomizer part does not seem to want to
go into position...it is usually just a wee bit of crud on
it or in the carburetor body hole. Insert the
atomizer as squarely as you can after cleaning the hole and
atomizer, and it will install OK. Remember that ONE
end is slightly smaller than the other, and only that end
One should remove only the necessary
parts, then spray into all the jets (pilot jet, mixture
adjustment hole, bowl jet, central main jet assembly),
etc., with a strong
carburetor spray, and let sit awhile, then spray again in
every direction possible through those holes. I prefer Berryman B-12,
in a version
called 'Carburetor and Choke Cleaner' for this job.
This is a very strong solvent mixture that actually
dissolves most all of the deposits from gasoline, which
many other spray solvents do not! You might
consider spraying all the metal pieces, then flush with a
common spray brake cleaner or equivalent. I do
recommend removing the central jet assembly, it tends to
get cruded up, often with 'black' stuff. Be careful,
as has been cautioned above, when replacing.
Some Bing carburetors, such as the
R60/6 and R60/7, use an acceleration
jet assembly in the central assembly, these parts all come
out mostly at one time, same as those carburetors
ENRICHENERS...yes, a whole choking section on this subject:
The enrichener pieces are easy to mix up and get installed backwards...or get the left and right carburetor enrichener parts mixed up. A good rule is to NEVER do both left and right carburetors at the same time. You bike could ALREADY have them assembled wrongly. The enricheners be assembled correctly for the 'choke' to operate correctly; AND...in the FLOAT BOWL, the corner jet in the well must be clean and UNclogged, and the downwards teeny pipe should be good, and unsplit.
enrichener parts orientation....
The brass shafts that
operate the enrichener are stamped in the inner ends, L and
R for Left and Right carburetors. The stampings can
be a bit vague, see above. The late models (well after early
/5 CV carburetors) rotating thick metal disc has an
elliptical hole, and 4 smaller holes, one of those 4 is a
bit bigger. The holes MUST be clear, NOT greased
up! There are
numerous types of the discs, some will not be machined
with the elliptical hole through the disc...and different
holes sizes and arrangements may be seen.
If you were to have the LEFT carburetor enrichener unit off the carburetor, and put it in front of you, upside down...that is...you are facing the inner (disc) side...and oriented so the round protuberance of the outer casting is TO YOUR RIGHT, and the LEVER is UPwards to its stop...about 1:00 THEN, the elliptical hole of the disc is roughly opposite the upper left casting screw hole, say 11:00....and the 4 tiny disc holes are roughly to the lower right....say 5:00.
For the RIGHT carburetor enrichener unit, as in these various photos, for the SAME orientation of casting and lever...the disc is REVERSED...that is...the 4 holes are to the UPPER LEFT, and the elliptical hole is to the lower right.
Here are some photos that will further explain things:
The above photo, marked WRONG!! has the dimple in the wrong direction. This MAY be necessary if your DISC/shaft is wrongly assembled by the factory!
Later model Bing CV carburetors have two-piece cable levers. It is possible to install the two metal pieces WRONGLY. It is annoyingly EASY to overlook this, and you won't notice until you have the carburetor fastened to the engine. Lever parts can be installed upside down AND/OR reversed in position. In BOTH Left and Right carburetors, the part that has NO notch (no slot) for the installation of the cable wire, goes onto the carburetor enrichener shaft first, with its offset facing the carburetor body. The outer part, that DOES have that notch (slot), can be installed wrongly, flipped-over if you will. Install it such that the notch does NOT face upwards during cable operation.
Here is a photo of how the later
model levers look when
installed properly; not a great photo, but you CAN see
the SLOT in the top part for the inner cable. The shaft nut and waverly locking washer are not in this photo.
This levers arrangement applies to both the enrichener and the throttle.
NOTE that for a
smooth AND PROPER enrichener operation, the enrichener needs to be
faintly lubricated, cables good, and operating lever cable
lubricated (IMPORTANT or cable can break strands!)... and if you have them, the T barrels under the
fuel-tank where the one cable from bars splits into two, in good
condition. There is an O-ring internally on
later enrichener models. I lightly silicone-grease that O-ring.
IF you are worried about using too much silicone grease on the enrichener disc, use silicone oil spray on the enrichener innards. When I use silicone grease on the disc I use it very faintly wiped with my fingertip to a very thin layer.
Whilst on the subject of enricheners/chokes, understand that in cool or cold weather, full choke may be needed for starting AND, very contrary to all the 'books' nice verbiage, you MAY NEED to manipulate the throttle during cranking.
In one version of Clymer's manual that I saw, in the early
section on how to start your motorcycle, Clymer's has the
operation of the choke lever (on the early models where
said lever is on the clamshell of the air cleaner housing),
BACKWARDS. The truth is that the
lever must be HORIZONTAL for the choke to be OFF....and
DOWN for choke ON.
The enrichener (choke) is held to the carburetor body by 4 screws. These screws are infamous for loosening. If the carburetor is still on the motorcycle, I recommend, that once the throttle and choke cables are removed from the top of the carburetors, that you loosen the carburetor adaptor clamps and rotate the carburetor to allow the tightness of these 4 enrichener screws to be checked. If loose, either tighten; or, remove and use a wee drop of Loctite blue and then tighten them. They CAN be tightened without rotating the carburetor, but it is typically a big hassle, even with several types of offset screwdrivers. If you take the enrichener screws out, clean them and their holes, and use a small amount of blue Loctite on the threads before tightening. BE SURE that the gasket is OK....the gasket tends to get sucked in, or otherwise distorted, if the assembly gets a bit loose. I recommend the faintest possible smear of some sort of NON-silicone gasket sealer on both sides of the gasket and the metal surfaces. REALLY faint! Gasgacinch; Permatex Form-a-gasket (non-hardening), etc. NO RTV HERE. The reason is not to prevent leaks directly, but to prevent the gasket from sucking-inwards, which then DOES cause leaks.
***Do not think about removing the throttle butterfly valves unless the shafts are really worn or leaking, as they are O-ring sealed, the screws peened, and the shafts can still be leakproof with a fair amount of side play due to the presence of the O-rings. To test for leaking, spray the shaft area from the outside of the carburetor, where the throttle lever attaches, with brake cleaner, while engine is idling. The idle speed must not change. If you do change the shaft O-rings, DO coat them, a bit more heavily than faintly, with silicone grease. They will then last almost forever, and operate smoothly. If you DIP the carburetor into a cleaning tank for any period of time with the usual harsh carburetor chemicals as used by professionals, you will HAVE TO replace the shaft O-rings. If the shaft is removed, then you must decide on the screws, to replace or not, to peen or Loctite.
****NOTE!!!>>>>>The butterfly can be put in backwards. Do NOT!!!! That is why I previously said to mark the butterfly!..top, rear...or similar. This is a CRITICAL point. The fitment of the lower edge (and the sharp shape at that point) of the butterfly is critical where it comes close to the the idle passageways holes at the carburetor bottom. Putting the butterfly in backwards will eliminate any chance of proper off-idle throttle performance. This is doubly important with a dual plugged machine in which the butterfly is more closed at idle. If you install a butterfly wrong, you will NEVER have a good stable idle. When installing the butterflies... as you slowly tighten the two screws, you must lightly press the butterfly with a finger, into the main carburetor bore, to align the butterfly...it is important that it fits the bore very evenly, and for minimal clearance (shine a light through the carburetor as you look from the other side).
The needle jet, which looks like a
machined brass tube of two basic diameters, and is often
marked with a number, such as 2.64, 2.66 or 2.68, fits with
the small tube portion upwards and its slightly curved
[internally] end downwards. Above that part is the
atomizer, which is a machined brass part of three differing
diameters, the slightly
smaller diameter goes upwards and fits through AND
INTO, the carburetor venturi (throat), and its
lower portion has the holes. On RARE
occasions this part might not seem to fit and does not seem
to want to poke up through the carburetor into the venturi.
If the smaller diameter end is up, the side-holed end down,
this is correct, and you may have the part slightly tilted,
or, tilted and under a tad of too
much pressure from the 10mm wrench area below. You
can install that atomizer by itself, and hold it IN the
throat, perhaps using a toothpick to get it properly into
position and then fingers to hold it in the throat, as
you assemble the lower parts.
The central jet assembly O-ring, with
the faint smear of grease, will reduce friction, and you
should be relatively gentle on the force you use on the
10mm wrench, just barely tight. Antiseize or silicone
grease on the brass threads make for less
corrosion and seizing possibilities. Remember that
the carburetor body is made of a soft and not overly strong
material....zinc probably. The danger is in cracking that
central carburetor boss. I grease the threads
lightly, silicone or anti-seize. Those
that over-tighten the central jet assembly, and fail to use
a lubricant or anti-seize, are asking for seizure, years
replacing rubber O-rings which you must push over threads,
you might have the thought that the threads might cut the O-ring...yes, they
could. A simple way of avoiding that
possibility is to not only grease the parts with a very
THIN layer of silicon grease....but to wrap a single layer
of any sort of tape around the threaded part, and THEN
slide the O-ring over it!
When installing or removing a slide needle, the most common type of needle is the twist/push-pull/turn type. For them, the proper method is to clean them and your fingers, so they both are clean and dry, and grip the needle tightly with thumb and forefinger, and rotate left or right, pulling slightly downwards or pushing upwards. EACH 90 degree rotation will allow ONE needle notch of change (if also pushing or pulling). UNDER NO CIRCUMSTANCES BEND THE NEEDLE. Rotate one direction, then the other, as required. Some may find that a thin piece of leather will help. NEVER use pliers!!! ONE (1) 90 degree rotation per so-called needle position!
Be sure both carburetors have the needle sticking out of the slide the same amount. Use a caliper, and measure closely. ***I HIGHLY recommend that you check the slides/needles for distance, to be sure they are the same, as well as to write down the distance, BEFORE removing or installing or changing the needle position. You cannot 'see' the needle position, it is done by feel, and having a measurement (you need to be accurate to maybe +- .015") may save you some considerable hassles. I measure them with a common vernier caliper. You can measure the underside of slide-to-tip distance, or, the distance from top of slide assembly 'tube' to needle tip. Needle position (there are typically 4 positions available) is measured from the top slot position of the needle. Most needles are in the #2 or #3 position from the top.
The other, later type of needle is not held in by the hidden clip in the same manner. There is a screw in the top of the slide. Remove the central flat-head screw from inside the slide, and turn the slide over. The needle should fall out the top into your hand, with a little clip on it around one of four positioning slots.
NOTE!....The SLIDE needles should be replaced at the 60,000 mile intervals I recommend, or tad sooner, with the associated needle jet. There is a particular problem with the aluminum or similar needle material on some 1985+ models, in 32 mm size. There may be some other carburetors with this problem. The NEEDLE grooves WEAR, due to the type of metal used. If the groove wears enough, the needle will not deliver the properly metered fuel. Watch for this, it is little known. Replace the needle and the clip! You can get weird symptoms, even backfiring, if things wear enough. Check BOTH carbs!...they do not, for whatever reason, wear at the same rate.
The carburetors should be mounted
squarely to the motorcycle. View from the top, and a few
feet to the rear of the bike. Do NOT tilt the tops
towards, or away, from the motorcycle.
CARB TOP STAINS:
LEAKY TOP PLUGS:
HARD STARTING, maybe ONE carb
does not work well initially, then works OK after engine running
& throttle opened:
If you have done most everything, and you have problems starting the bike, consistently hard starting, or maybe ONE carburetor is acting up, that cylinder not firing (maybe even until engine warms a bit) and throttle is opened.....check that the enrichener was properly installed, no matter if the dot-dimple on the shaft looks correct.....and if still a problem.... see if the butterflies were properly installed. Not only is this to include loosening the screw whose bracket keeps the shaft in place, but loosening the butterfly screws (a problem if peened, if not, when tightening, use Loctite BLUE), and be sure the butterfly will completely seal to the carb bottom.....and tighten things again. If the butterflies are reversed, you will never get proper operation.
If you have a R75/5 that is particularly a bear to start (or, one carb is not working at startup), and everything else checks out fine, be SURE to check the slides, to be SURE they are BOTTOMING fully, and not hung up slightly. Install the springs above the slides. This problem is rare, but has been seen on them, and VERY rarely on later carbs. Polishing the slides and inside carb body can help. There is a very complete article on this website about the R75/5 carburetor problems: http://bmwmotorcycletech.info/earlybingR75CV.htm
Sometimes there are complaints of hard-starting bikes. The owners have checked everything, including valve adjustments, compression pressure, spark plug wires and caps, coils, everything....and the bike still does not start OK. Check the slides on CV carburetors, be sure they are fully bottoming.....there is a spring on top of the slides on some models, to help with this.
I have information on this website ....originals of some Bing documents, some of marked-up copies, crude, but useable...all of various Bings sheets on installation and adjustments of the independent floats KITS. Here is a hyperlink: Bingindependent.htm
Be gentle and careful about doing any
bending. Float level affects richness-leanness and gas
NOTE and HINT: The band clamp at the carburetor throat inlet USUALLY should have its adjustment at the TOP...or, at least not at the bottom. The curved intake plastic tube fits in most models only in one direction. If fitted wrongly, things do not line up well. If the band adjustment is not above the bottom, the breather output oil may drip on your foot, depending on if there is a slit or not on the tube; this was particularly so on the earliest models. The intake plastic tube can be slotted for easier use.
Additional information on Bing CV carburetors will be found at http://bmwmotorcycletech.info/bingcv-2.htm
to 12-07-2002: mostly
© copyright, 2014, R. Fleischer