Petcocks, fuel filters, fuel tanks,
fuel flow amounts, re-fueling,
clam-shell models choke lever
operation, fuel hoses, etc.
© Copyright 2018, R. Fleischer
Each petcock is fastened to the tank by both right hand and left hand threads. As you rotate the large "nut" CW (facing from below), that tightens the nut to the tank while at the same time it brings up the petcock. The petcock large nut has to be FIRST engaged the proper amount onto the petcock BEFORE screwing it upwards to begin to engage the proper amount of tank threads. If you have never done this before you will have to fiddle with this until you get the right amount of petcock and nut threads assembled ...to start ...and finish...the petcock-to-tank fastening process. Once you learn, it is easy. You want approximately the same number of threads engaged on both the petcock and the tank after fully tightening.
BMW has used numerous petcocks over the Airhead production years. There are five types of petcocks normally seen on our Airhead motorcycles. All except the /5 bullet types are easily re-buildable. Usually this means that you unscrew some knurled or slot "nut" at the handle area (after removing a black trim cup, if it is there on your version), and you can replace a gasket that might be bad, or clean and very-faintly-lightly silicon grease the moving parts. You then have a much smoother operating petcock. On some there are one or two dimpled discs, which can be repaired with a shaped punch, lightly hit, for a better detent action; I usually don't bother. These discs have a locating tab. They can confuse, so take notice of how they were assembled as you take things apart. You cam figure it out, if you forgot to take notice.
Our petcocks have a Reserve function. Except for the bullet type, photo below, the handle long portion upwards towards the tank is the reserve position. Horizontal (either way) is always off. German "AUF" printed on the body/cap means on, not off. Handle lever downwards means on for the main part of the tank.
Early /5 Bullet Style Everbest Petcocks were different in how the handle indicated fuel flow, & the rotating handle affecting gas flow from was in the opposite way from standard piping flow. Standard industrial and home piping flow indication by a valve lever is that the lever handle points to the tank or to the outlet, for flow. Here is a sketch of the original slash-5 bullet petcock:
HINT! On the motorcycles with the above petcock and the clam-shell choke lever/cables, the choke cable tends to rub the underside of the petcock bullet area. The cable has been known to wear through the petcock! I suggest you add a piece of rubber hose over the cable where it might rub the petcock.
These early /5 petcocks, on the engine side of the handle, look something like a very large tapered round bullet. They are snapped together, and it is very difficult to take them apart without breaking them, but this often can be done if you go about it correctly. They have an easily removable nipple at the bottom, inside of which is a small fuel screen. See the photo, above. Because they are the Classic /5 petcocks, you may want to try to overhaul one. Repairing one is a bit time consuming; but, if successful, you can retain the classic look of your /5. While I personally would not bother try to fix an early bullet style petcock, Purists think differently and may well want the motorcycle to be absolutely original in appearance, so trying to rebuild a bullet-style Everbest may be worth a try. You can sometimes find brand-new bullet style Everbest petcocks on Ebay ($$$). I'd not be surprised to find out that they were being made again, and you can ask such as Vetch, see www.benchmarkworks.com, see the next paragraph. Some have been able to force-twist the /5 Everbest petcock apart for repairs. If that fails, you can do the UNcrimping. You may want to read all the articles I link to. I have had problems with links to sites showing how to overhaul the Everbest. The links change, making them worthless. I check all these links now and then. I thought it best to copy and display Vech's information, below.
I copied the following from Buchanan's site, who had copied it from Vetch. The author, as noted, is Craig Vechorik, AKA VECH. Craig Vechorik's website is http://benchmarkworks.com, where he has decent information on how to rebuild one. The problem is finding the article. Vetch's website is generally not set-up for internal hyperlinks nor listings of such that are easy to get to. However, this MAY work: http://www.benchmarkworks.com/articles/howto/petcock.html If it works, you may want to read it, and then what I have copied from Buchanan's site, below:
Rebuilding Everbest petcocks, Craig Vechorik:
Everbest petcocks (used up to the /5) ARE rebuildable, I do it all the time. Buy a roll of 1/8 sheet cork at an auto parts store. You must trim at the body a bit with a knife, to cut away a bit of the crimp they put in the edge of the hole that the plug of the valve fits into. Then put the handle in a vise, and pull and twist the body, CAREFULLY, so you don't break the handle off, and you will pull the plug of the valve, and the retaining washer ( which the crimp in the body holds) out. Clean out the body with a round plumbers wire brush. Sand the plug LIGHTLY with 600 sandpaper. Then you cut out a piece from the cork sheet that measures 1 29/32" x 1 1/6". Make sure that your cut piece is square and accurate. Grease up one side with wheel bearing grease, and roll it into a more or less cylinder, and shove it, (with the open seam to the side of the body) into the body. Be sure to get it all the way in, and square. Then grease up the plug and press it in. It will take a good bit of force, and I do it with the aid of a vise. When you get it all the way in, take a small screwdriver, and a light hammer, and crimp the body just a bit, to hold the retaining washer in. Then turn the petcock to the on position. (it will take a good deal of force at first, 'cause it WILL be tight.) and find a drill bit that will fit down inside the brass supply tubes, and CAREFULLY drill the cork out of the OPEN hole and the hole on the output side too. Blow out the crumbs of cork with compressed air, and turn the petcock to the reserve position, and do it again. After you put it back in use, if you ever take it off, do not allow it to ever dry out. Put the petcock in a jar of gasoline, with a tight lid.
You have nothing much to lose if that method does not work, as you can always substitute a later petcock, so here is another way to go about it:
The early /5-style of petcock is press-assembled, and staked. To disassemble it, you must trim away the body slightly, of the crimp area. Do NOT remove excessive material in that trimming. Then put the HANDLE of the petcock in a soft jawed vise, and pull and twist the body, and it will come apart. You will need some 1/8" thick cork to finish the overhaul job. See also link for rebuild parts. Most auto-parts stores have some cork. You could use a piece of gasket material, etc. You will have to cut the cork to fit, and then SILICONE grease it, roll it sort of cylindrical, insert it into the body...seam towards side...install squarely. Grease the removed plug part and install it...it will take considerable pressure to do this. Now you need to crimp the area so it cannot come apart on its own. After that is done, turn the handle (fair amount of force probably needed) to ON position. Drill down the main tube through the cork, and the outlet too. Blow out the cork dust. Repeat for the reserve position tube and outlet. Clean out, and reinstall.
Here is a link to Bing Agency's petcock page, useful for the photos, etc. BMW dealership prices may be LESS.
ALL the petcock styles except the bullet nose /5 type are fairly easy to take apart, clean, and repair...typically this is done because they have begun to either leak or are stiff operating.
Petcocks using CORK inside for the active element can often be reclaimed to good operating
condition after being dry for years by simply soaking in very hot, even near boiling water.
NOTE: The original "straight" type petcock used early-on after the bullet petcock is no longer available from BMW dealerships. Check out this website page for availability of that type:
http://www.motobins.co.uk/bmw-parts.php?model=R Series 2 valve Twin
Have clean surfaces and a good grunt on that large outside nut....with equal threads being engaged when fully tightened. This applies to all the BMW Airheads petcocks when installing them.
Most other petcocks have the screen inside the outlet, so remove the outlet part to see and clean the screen. These petcocks have the outlet straight down, and have a separate smaller nut at that outlet, so as to remove the outlet stub and get to that filter. That does NOT mean that all straight down outlets have screens. Easy to find out, simply remove the hose, and unscrew the lower nut, see if a filter there...or a place for one, the previous owner could have left it out. The outlet, when the removable type, is called a tap spigot, or??, and they are available, or were, in both metal and plastic. Guess which one does not like to be bent sideways when removing a hose? Any spigot may have a groove in the part that fits up to the petcock, hidden by the nut...that groove is where the filter screen fits, some types of filter screens had to be hand-formed to fit just right, others had stiff end structures.
I cannot emphasize enough that you SHOULD ADD an aftermarket filter between any petcock and the carburetor. More later in this article.
TWO types of petcocks do not have an outlet screen filter, these have non-removable horizontal fuel
outlets so there are NO nuts on the outlets, the outlet spigot is part of the casting. One of these will
look similar to the late version but the threaded ring, which is still cross-slotted, has NO outer edge knurling,
HAS a radial slot and has the internal operating 'gasket', with the ports to allow the fuel flow, made of
Change that to rubber part #16-12-1-235-551. The cork can swell and make the petcock
stiff to operate, and it can also shrink, and cause leaking. GENERALLY that cork to rubber change is
for the USA and Canada shipped models R60/6 through R100S. There are sub-variations of these
petcocks, in how the outer ring appears, tightened for pressure, or not, etc. The last version of these
had outer edge knurling and had the rubber part AND a rather stiff coil spring, and seals better. These horizontal outlet late-style petcocks are HANDED. There is a left hand side & a right hand
side. This information is hardly noted anyplace but here by me, as is why TWO right sides are used
on some bikes.... In mid-1980 & later, BMW added a tank fumes solenoid valve & a fuel flow solenoid
valve. These are located inside the cover that fits over the starter motor. There are holes in that
cover for hoses, etc. Because of this arrangement, BMW used TWO EACH "Right Hand Side"
petcocks. If you remove some or all of these solenoid parts, you MAY want to purchase a LEFT
hand side petcock (for the left side, of course!), which COMES with the newer bonded filter screen. If you install all petcocks so
their OUTLETS pointing REARWARDS, then the curve of the fuel hose will be nicer, shorter, & the
hose might last longer. However, that requires one RIGHT type & one LEFT type.
I usually find the rubber disc simply in need of a cleaning (with the rest of the petcock), & I re-use them, with a VERY FAINT smear of common dielectric grease (a silicone grease) on the rubber & all the moving parts. There isn't anything in any of 'the books' about overhauling them, AFAIK. Occasionally the dimple that locates the position has worn, I normally just forget about it,
I can tell when the handle is fore, aft, up, or down! ...I don't need a click/feel to tell me! BUT...you CAN
reset the dimples with an appropriately shaped punch. When re-assembling, push the body onto
the 'nut', not the other way around!... as the spring is very stiff. I do it with the 'nut' again clamped in the brass or aluminum protected vice jaws,... otherwise you will need leather gloves or your fingers will not like the knurling. Before assembling, be sure you have lubricated the handle, flat rubber disc, spring, and inside
the metal cap; all with silicone grease. If you do it all as I say, you may go MANY years before having to repeat the cleaning/lubing.
Always service the fuel tank and petcocks by REMOVING the petcocks from the tank. You NEED to see what grunge is there, thoroughly clean the tank, etc.
The various inlet and/or outlet screens should be cleaned with your yearly tank cleaning. There is no need to disassemble the petcock internals until action is overly-stiff....THEN, except for that cork mentioned well above to be changed to rubber, there is usually nothing to do but disassemble, clean, and apply silicone grease very thinly, and reassemble. Obviously you do not want so much grease that you plug the disc holes. You DO need the grease on the handle inside flat area and the face of the 4 hole rubber washer...do this very sparingly. Silicone grease may be called Dielectric Grease at your AutoParts store....and it has many uses on your motorcycle. The petcocks will remain very easy to use for a very long time after you clean & FAINTLY lubricate them.
Except for the early /5 'bullet' style petcock, the other types of petcocks are easily taken apart. Sometimes, on the LATER, non-Germa ones, it is a bit of fun to re-assemble. HINT: one needs a good grunt to push the threaded nut & handle assembly back into the body to get its threads started properly. Some folks think this is easier by using a bench vise (carefully, don't over-squeeze!) on the NUT portion, & pushing the petcock portion, ...SQUARELY!!...to the nut. NUT here means the knurled or slot part (possibly under a black plastic cover, which pries off).
For the petcocks with or without a black plastic cover around the lever area, slowly remove the black cover. Pry evenly, all around, a bit here, a bit there. You can use a small piece of wood or plastic, or ? to avoid marring. You might want to put the whole petcock in moderately hot water, and use a wood or plastic tool. The water will soften the black plastic cover, expand it a bit, and make it easier to remove....and the plastic/wood tool is less likely to gouge or mar the material. There have been instances of loose caps, where someone has glued it to the petcock, just be aware of this, as it may take more work to get the cap off, which is needed to remove the handle and innards. Underneath the plastic cap you will probably find a sort of knurled edge that must be gripped in order to unscrew the metal cap plug from the body. I made a special tool for this about 30 years ago, can't find it to show you a photo, but you CAN grip the edge lightly in a vice & then rotate the rest of the petcock around it. It is better if you had some ROUND JAWS, perhaps from a good drill chuck, or a lathe chuck. The black outer cap hides your messiness, but why not do the job carefully & not mar the metal? My present method is to use two pieces of BRASS or ALUMINUM, which are soft, and works well with the petcock knurling, in the vice jaws. It can be done so marring the knurled 'nut' does not occur.
If you have a petcock that has not been serviced in a very long time, and perhaps has been exposed to moisture or near the seacoast, & the knurled ring nut will not remove, or not hardly easily, then I suggest you heat the petcock to near water boiling temperature, and then remove it from any heat source, & place the entire petcock into a container that has a reasonable amount of very thin but warmed penetrating oil. You want the penetrating oil to get into every part of the petcock. Work the lever a bit, then let it sit for a day, then work the lever again. I do this every day for about a WEEK. After that, I can usually remove the knurled nut in my vice, using brass or aluminum protective jaw facings.
Some versions use a 'nut' with slots, and you can improvise for that. I made a tool.
Pay attention to any indexing disc(s) inside & how arranged. Which side fits the other side, where & how the tabs fit, which disc goes back first, when re-asssembling.
As explained earlier in this article, that large nut tightens the petcock to the tank and at the same time it also has a reverse thread on the petcock, so the tank and petcock tighten together properly. When assembling to the tank, you start with the nut in an estimated position on the petcock. The idea is to END UP with ~ equal amounts of tank & petcock threads being engaged. DO NOT GOOF!...you MUST have approximately equal threads engaged. If you engage only 1 or 1-1/2 threads or so, you will damage the threads.
I usually find the rubber disc simply in need of a cleaning (with the rest of the petcock), & I re-use them, with a VERY FAINT smear of common dielectric grease (a silicone grease) on the rubber & all the moving parts. There isn't anything in any of 'the books' about overhauling them, AFAIK. Occasionally the dimple that locates the position has worn, I normally just forget about it, I can tell when the handle is fore, aft, up, or down! ...I don't need a click/feel to tell me! BUT...you CAN reset the dimples with an appropriately shaped punch. When re-assembling, push the body onto the 'nut', not the other way around!... as the spring is very stiff. I do it with the 'nut' again clamped in the brass or aluminum protected vice jaws,... otherwise you will need leather gloves or your fingers will not like the knurling. Before assembling, be sure you have lubricated the handle, flat rubber disc, spring, and inside the metal cap; all with silicone grease. If you do it all as I say, you may go MANY years before having to repeat the cleaning/lubing.
Always service the fuel tank and petcocks by REMOVING the petcocks from the tank. You NEED to see what grunge is there, thoroughly clean the tank, etc.
Now and then I hear about someone with the wrong idea on how a petcock works. As a general rule for all plumbing and piping, flow occurs when the handle points in the direction of the pipe, NOT when at 90° to the pipe. Your petcock MIGHT NOT be marked ON, OFF, RES (reserve). It MIGHT be marked AUF and ZU. AUF does NOT mean OFF! AUF here means MAIN tank portion is ON! This is not as laughable as you may think! ZU means OFF (closed). Thus, when the handle lever is downward, the main tank is being used, when upward you are using the main tank and reserve, & when horizontal you stop the fuel from flowing. HORIZONTAL IS OFF!
NOTE! Early bullet-style Everbest Petcocks do NOT work up/down by the long handle end in this standardized way...the short end of the handle has an arrow-type tip.
Aside note: Some Clymers books are WRONG on the position of the handle for the
(enrichener) ON CLAMSHELL AIR CLEANER MODELS. That means pre-1981. The correct information is that when the clamshell handle is horizontal, the choke is OFF. When the handle is downwards from horizontal, the handle points in the direction of extra fuel richness, towards the carburetor. Clymers had this backwards! Clymers wrong
information has obviously caused problems with starting and running!!!
There are two tiny diameter plastic or metal pipes "straws" of UNEQUAL length going upwards from the petcock into the tank. Once in awhile these are replaced due to cracking on the plastic ones or they are broken, etc. The TALL one is for the regular main tank outlet, NOT the RES outlet. The short one is just tall enough to keep bottom rust, water & other bad stuff from getting into the petcock on the RES position. SOME have shortened it, by half is OK, it is NOT OK to remove it entirely.... you will hardly gain much additional usable fuel...at best maybe 10 ounces... & you may get rust and other nasties into the petcock & the carburetor.
When the petcock is turned to the off, horizontal position, both tiny pipes are closed off from gas flow. When the petcock is in the main tank ON (down on all but /5 petcocks) position, fuel flows from the tank into the tall pipe until no fuel is above the tall pipe level. Once the fuel in the tank (on THAT side for two petcocks tanks) is at or below the tall pipe level, you get no more fuel from that petcock. Putting the handle on RES will start drawing from the reserve portion of that side of the tank. Thus if you wanted to, you could run on one petcock, main (down), until the motor runs that side dry on the MAIN, then turn the other petcock to main (down) position, and then use two more RES (reserve) positions. Up to you how you use the petcocks. If you have a one petcock model, you have no such options.
I recommend using both petcock's ON, for 800 & 1000 cc models.
If you have a hotted-up motor or 800 cc or 1000 cc engine, hotted-up or not.... & a single petcock tank, you SHOULD enlarge the hole through the petcock petcock, for additional flow at wide-open-throttle. Do that to the straws too. Here is more information:
For a modified engine (enlarged, or otherwise horsepower is increased), if you have a single outlet port fuel tank, you probably should change to a dual-port type, OR, modify the petcock on the single outlet tank. The stock single petcock will not flow enough fuel at extended W.O.T., particularly on an R100 engine. Careful drilling & modification of the petcock will work well. You CAN retain the in-tank thin tubes leading upwards from the petcock, by drilling them out a SMALL AMOUNT. A = π rČ
That is not easy and you may wish to remove them, drill the petcock larger, all the way through, & fit larger inside and outside diameter tubes to the petcock. I have had GOOD LUCK with carefully reaming/drilling the existing stock straws!! A small change in inside diameter is a large change in flow. Be sure to measure the improvement at the carburetor (bowl off, measure cc per minute or shorter period). Using a one-petcock fuel tank, modifying is almost a must for a R90 or R100 engine, and not modifying is marginal for WOT even for the R80 engine size. A few hundred cc per minute per carb, measuring with BOTH carbs float bowls off, is a good idea. If you have to, drill out other items, including filters, T adapters, etc. Remember: a SMALL change in inside diameter makes for a rather large change in FLOW. THE most restrictive item IS ALMOST ALWAYS THE PETCOCK AND ITS FUEL STRAWS. If you carefully use a sharp and LONG drill bit, you CAN enlarge the inside of the straws, right into the petcock, & this really does work well. You need enlarge only a small amount. More on this, somewhat below.
The actual length of the stock petcock 'straws' themselves is not the same in all models. The dimensions I show here are PROUD OF THE SURFACE THE STRAW IS PRESSED INTO and will work fine on all tanks. The straws can be metal or plastic. If yours are cracked, you can usually use tiny diameter copper tubing available at hobby shops. If you need to, sand the end area diameter of the metal tubing you purchased, and SLIGHTLY chamfer the down side very end ...both for ease in assembly and proper fit. Consider using a SHORT straw of 0.935" (23.75 mm); and 3.27" (83 mm) for the TALL straw.
Some have wanted to shorten or eliminate the short straw. Yes, you CAN shorten the short straw and gain a SMALL amount of usable fuel. My advice is to NOT eliminate that short straw, certainly leave at least 3/8" proud of the metal. You will need to add a small amount to these various lengths for the straw itself, as they are pressed-into the petcock. There is NOTHING critical about the final length of the straws.
If the tank is not cleaned regularly, perhaps yearly, especially if you don't fill up after every ride, or live in a high humidity area, the tank may accumulate a fair amount of WATER, whichWILL ROT OUT YOUR TANK BOTTOM. SOME water comes from the fuel itself; MOST comes from inside-the-tank-walls condensation as fuel & tank cools after you park the bike. This is particularly true in high humidity areas, where you can see dew on the tank, seat, etc., in the morning. It is very important to clean the fuel tank of any water: it WILL rust out at the bottom! The 'red' internal coating on these tanks is now quite old, & typically has some deterioration, so heed my words about cleaning the tank & filling up after your ride.
CLEAN THE TANK TOTALLY, yearly.Clean the filters at the petcocks regularly; replace aftermarket pleated paper filters when flow lessens noticeably; or, on a schedule. If a fuel tank is very old, grungy, full of sediments, etc., I recommend using a high pressure car wash wand, with soap, on the tank insides, then wash the tank & dry it. Rust can be treated with phosphoric acid mixture (or the tank relined, which is a HUGE labor-intensive chore).
It is helpful to fully refuel before the bike sits overnight.That helps with dew/moisture otherwise condensing inside the tank on the walls that would not be covered by fuel. The water will condense into globules, fall to the bottom and cause the metal tanks to rust or rot out...yes, rot, even on aluminum tanks. NOTE that 100% filling to the brim is NOT generally a good idea....due to pressure effects from temperature changes, particularly if the tank is in the sun. Think about your usage, and your filling.
Many folks add an additional aftermarket filter below the stock petcock. I DO recommend that you DO SO. Sintered metal types are OK, as are treated pleated paper types. SCREEN types do very little good, as your
petcock already has a screen. This also applies to very fine screens, which do only very slightly more cleaning....and can be restrictive, which is NOT good.
The Napa 7-02323 & FRAM G4164 are similar, although not so in quality, & are actually replacements for early Volkswagen filters, VW ZVW262101....but are also used on many small garden engines, etc. A.C. filter GF453 will work, but it really is too large, its diameter is nearly 2"; over-all length almost 5", and its stubs are single step with 1/4" bump. I recommend against this item & its size unless you have to use it, or have a very much deteriorating tank.
NOTE: Many plastic bodied filters have a nice feature: The input and output stubs are dual-diameter stepped, so the filters will fit whatever hose you are using. Do install them vertically.
NOTE: The 7-02323 is very similar to the slightly cheaper Napa 3011. The 7-02323 is part of the Napa Marine line of products, and has MORE pleats, and somewhat better made. The 3011 has less pleats. Either will work OK.
SOME filters have arrows pointing in the direction of fuel flow; more often filters do NOT have markings for flow direction. The input end, which goes towards your fuel tank petcock, is the end that fills the OUTER area of the filter. The output end is the connection to the filter element INsides. This is NOT critical on most types of filters, although most that ARE critical ARE marked. However, installing the filters in the direction I have noted will give MUCH longer filter life.
Napa, and seewww.napaonline.com, has changed its numbering system slightly. If trying to see a photo or? of the Napa filters, if their search engine does not display 7-02323, try entering it as 702323....and it may come up as SME-702323 or even SME702323. Same for the 702357. Don't know about the 3011.
All these filters work best VERTICALLY, but are OK horizontally, but have much less hose & vibration strain on their plastic if used vertically; besides using more of the filtering element when vertical. DO NOT fail to replace these filters now & then & do NOT fail to clean the tank regularly & clean the petcock filters now & then. Remember that later versions of the petcocks have in-tank filters. If your tank is fairly clean inside,
you may get 20K (or more!) miles on aftermarket filters before they need replacement or cleaned, if that is possible on your types. The clear plastic ones, depending on make & model, sometimes can visually show you if they are getting clogged, by looking at the paper pleats & sediment. DO NOT DEPEND ON A VISUAL INSPECTION.
Aftermarket external filters are a big help because it takes hardly anything as thick as a human hair in the carburetor to cause problems.
If fuel flow decreases enough, your engine will run lean & potentially hot, might stumble some, & a lean running engine can be harmful to your bank account!! That is one of the reasons I prefer you NOT use the tiniest of these filters.
I DO advise modifying the petcock on single petcock tanks, if used with modified engines, or, any over 600 cc.
Fuel hose recommendations has been moved to item #11 in
http://bmwmotorcycletech.info/fuelmiscl.htm HINT: Perhaps once every year or three you should flush the bowl jets, pipe, etc., with something STRONG, like Berryman B-12 CARBURETOR AND CHOKE spray, using the wand, and replace the bowl gasket now and then.
When you do this, don't leave Berryman B-12 in the passageways for long periods of time; a few minutes is fine. THEN re-spray
the passageways with a mild cleaner, even brake cleaner is OK.
Failure to at least empty the bowl can let 'stuff' get into the idle pilot jet, which has an exceedingly small hole. Sediments of various types, plus water, can mix & plug the tiny corner well bottom jet. Then the enrichener (on the CV carbs) won't work properly. The bike may be very difficult to start if the condition is severe. A bad bowl gasket, especially at the CV enrichener down pipe area, can also make your enrichener (choke) operate poorly.
The central jet assembly in the CV carburetors has a tendency to collect black grunge. Remove the entire assembly & clean it now & then...>>be careful upon reassembly not to overtighten, nor tighten the assembly against the needle tip....!!!.
The upper-most part fits properly only one way.
Perhaps once every year or three you should flush the bowl jets, pipe, etc., with something STRONG, like Berryman B-12 CARBURETOR AND CHOKE spray, using the wand, and replace the bowl gasket now and then. When you do this, don't leave Berryman B-12 in the passageways for long periods of time; a few minutes is fine. THEN re-spray the passageways with a mild cleaner, even brake cleaner is OK.
GAS CAPS: venting, various failures, locks and keys, ETC: See article 1B
©Copyright, 2014, R. Fleischer
Last check/edit: Friday, February 23, 2018