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Bing CV Carburetors, overhaul, etc., Part 1 of 2 parts

There is no specific article on this website for Airhead "slide" carburetors; only the articles for the "CV" carburetors.

ALL of the Bing carburetors, with STOCK floats, which means the 1/26 models as well as the 32 and 64 series, have a specification for brand-new floats, of 10 grams.  After they have been in use, they MAY get heavier.  About 13.5 grams is near the maximum.  For those with gunpowder or other scales, weighing in grains, 200 grains is about the limit.

Copyright, 2014, R. Fleischer


>>A basic mini-overhaul can be done with the carburetors in place on the engine. 
Quite frankly, this is often quite enough.<<


READ Article #6 on the R75/5 carbs....some really IS pertinent to all the CV carbs:

READ:     That is Part 2 of the article you are reading now.

For a well-done article...step by step...with 44 pictures....see BMWMOA magazine, BMW-ON (BMW Owners News), for March 2003, for an great Gary L. Smith.  You can probably get that back issue at:
From that main page, click on left side for Country Store, and then on the Country Store page, go to Back Issues.

I have SOME nitpicking on that article:
1.  See my notes in the article you are reading.
2.  Use faint amount of silicone grease on all O-rings and on enrichener parts (do NOT overdo this, you do NOT want to plug jet holes).
3.  If doing a complete overhaul, which involves removing the butterfly to replace the throttle shaft O-ring (be sure to silicone grease that one too!), be SURE to MARK the butterfly for correct refitting:  something like TOP, OUTER; or TOP, facing REAR...or something of that sort....BEFORE you remove the old one.  You can hope that the previous workman did not install yours backwards, because it can be fun to figure out unless you know what it is supposed to look like.   I ADDED, in the article you are now reading, on 05/14/2012, photos of what it is supposed to look like, and NOT look like.
4.  The article you are reading will have more complete information about orienting the enrichener parts.

Below is a website in which you can enter your carburetor model number, and get a chart showing all the component parts numbers!

The Bing CV carburetors are moderately complicated in HOW THEY WORK.  BUT, there are only a moderate number of places in these carburetors where you probably could run into trouble.   For the 'Newbie', I advise reading all of the carburetor articles completely through, even though you will not likely understand everything at first read.   Once you have overhauled your first Bing CV carburetor, you will probably wonder what all the fuss was about.


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:


FIRST section:   the floats, my testing, information on failures, alcohol in fuels, etc.
This is a LONG section, and is here for reference purposes.

The stock dual 'one-piece' plastic float assembly does not always fail by getting considerably heavier; yet when bad, it will sink in gasoline (essentially hardly any will be above the surface in a container of gasoline in which the float, without pin or anything else, is trying to float). Once it deteriorates and begins to sink, your mileage will get worse and worse, eventually perhaps with fuel flowing onto your foot. 

Floats are not consistent in how they fail, and that MAY be due to the type of gasoline they are used with.   New floats weigh about 10-13 grams.  A horrendous badly sinking old float that almost sunk totally was measured at 18 grams.   MOST stock white one-piece floats will get heavier as they deteriorate.   Once they are removed from gasoline and very thoroughly dried, which can take a lot of time, they may lighten considerably, and then not gain much weight if again put back into least for a month or two period of time for drying.

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.  This simple test will be explained later in this article.

Information from extensive testing on a large number of floats was FINALLY! completed, after many 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 quite a few 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 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.   HOWEVER, I hardly think I exhausted all the possibilities.  

A bit of background follows, then the float testing results.

Alcohol, ETC: Some additives are used as 'co-solvents', that is, adding them ALLOWS other additives to MIX with the gasoline, that might not mix by themselves.   Yes, this allows WATER to mix with the gasoline, among other things.   Some additives are used mainly for oxygenation purposes.   Theoretically, under some conditions, adding something that contains more USABLE oxygen, per unit of volume (or weight) will allow a fuller burning of the fuel.   Under SOME government mandated test routines, they lower the 'smog' output of the engine, BUT, they USUALLY cause a DROP in mileage, causing more smog from just that alone.  SOME types of emissions ARE actually increased per mile traveled...they are just not the one's the government agencies have a priority on. Use of alcohol (and several other additives) containing fuels will almost always result in a LEANER burning condition, generally meaning higher engine temperatures, and if severe, can lead to burning up pistons, problems with the valves, and even engine seizure.    While it is true that alcohol has a higher octane equivalency, using alcohol requires more VOLUME of alcohol.   In order to maintain more consistent burning, one really should change one's jetting (needle and main jet) to slightly RICHER, if alcohol fuels were used all the time, and the fuels were consistent in formula.  This would REDUCE gas mileage even more than such fuels do with the stock jettings, although driveability would be a bit enhanced.  ONE step at the needle JET (NOT one step of the needle clip!) is usually enough, plus 5 or 10 digits on the main jet.

Use of alcohol fuels is, in my mind, should be absolutely forbidden in PREMIX type of 2-stroke engines, as the alcohol and water can separate out of the oil, and the engine seize from lack of lubrication. In the Airheads, it is not a big problem at up to 10%, but alcohol CAN cause 'driveability problems'....poor throttle response, hiccuping, jerking, lousy warmup. If your bike is already lean running, and Airheads from the 1980's, especially those exported to the U.S. are like that, you might have WORSE driveability problems....or...overheating. Testing for alcohol can be done rather simply, but it is a PIA to do at every fillup, and this type of testing (mixing in a test tube, with water, see if water level rises) also will, unfortunately (or fortunately??) show up MTBE, and some other additives that absorb water. California's reformulated gasoline's are a problem, and this has spread to other States, although California has now phased out MTBE in every part of the State due to its disastrous effects, if spilled, on underground water supplies. 

Alcohol-laced fuel is now STANDARD in the USA, and it is typically difficult to find alcohol-free fuel, and when you do, it is $$$.

Some States require labeling the pumps, some do not, some only if the % of alcohol or ?? at some particular level or beyond. 

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 maintenance list!

Because of the horrible additives used in gasoline's today, gasoline can NOT be stored as long as it used to be, not even with an additive you purchase such as StaBil, although it does help. The gasoline will deteriorate, not good for tanks, petcocks, hoses, and, of course, the carburetors. It tends to gum up during that deterioration. 

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' 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.

Types of liquids I tested:
isopropyl alcohol, high % as well as mixed with water.
ethanol....medium %, as well as 154 and 191 proof..
above with varying water content as well as chemically dry (anhydrous).
toluol (toluene).
California MTBE gasoline.
Known standardized Chevron 91 octane fuel.
California reformulated alcohol added Gasohol.
leaded fuel.
motor oils.
a solvent consisting of a light aliphatic complex with naptha's, toluene, xylene, methanol, acetone and MEK.
common denatured alcohol.
MTBE high concentration.
a solvent consisting of toluene, n-butyl acetate, 2-butoxyethyl acetate, and a few other things.

I. Weight change (weight is in 'grains'; there are 15.43 grains per gram):
Used floats tended to be in the range of 185-255 grains when well dried out. After soaking for weeks in various chemicals/solvents/gasolines, one particularly bad set of floats was almost 262 grains immediately after removal from MTBE containing gasoline (allowing a couple of minutes to evaporate the surface liquid). This was a very bad set indeed. But this set was 255 as I received it. This means that whatever change happened to these floats, it was mostly permanent. Typically the weight change occurred during the use on the motorcycle, with only some more moderate increase when put in the various liquids. This suggests that the aging is very slow.   MTBE is only ONE of many harmful substances.  MTBE has been phased-out, due to water table contamination.

***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 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.  

II. Some special tests were made to determine if there was a shift in the concentration of mass. This WAS found to be so. This was not excessive, but combined with an over-all change in weight, was more prominent than might be expected.  A small change in mass movement, plus a small change in weight, would be enough to cause a float to sink a fair amount.

III. Change in dimensions: of each float assembly, both sides were measured for width and length. There was a small variation noted even with brand new floats. One surprise was that the dimensions changed very little from new.   I theorize that the outside of the float tends to harden some, and become slowly more impervious, whilst the nastier fuel components get inside and do their damaging work on the float inner portion.  

IV. Other changes: INternal discoloration was NOT noted on some, but the worst were ALWAYS discolored.   Almost no truly bad reported (by sinking noted by owner) floats were still white on the outside (although some were INternally a bit darker).

ONE SPECIAL THING WAS NOTED!! As the floats became worse....that is, they tended to sink in gasoline more and more...and usually became heavier.....the INside of the floats tended to turn into a somewhat MUSHY and almost granular mixture, even if left out to dry for a considerable period of time.  ONCE cut open, they would dry out, although this took a fair amount of time...several hours, and not fully for a few days. The OUTside tended to be a harder 'shell'. The conclusion is that whatever the exposure medium was, it tended to migrate INside and make changes to the contents, and generally INcreased the internal mass weight.   Mushiness and granularity was not the only change noted!...there was a small shift...mass movement to change the CG! The worst floats tended to have small voids in the floats (bubbles or similar). My suspicions are that something...perhaps something in gasoline I did not test for....may be modifying the insides of those floats, besides the fuels tested. It is also possible that the initial brand new float change to the interior is actually the effect of the things I tested for, but would take many many months.  There was absolutely no doubt that MTBE containing gasoline made the interior of the floats mushy.....but surprisingly, since Bing touts its dual-independent floats as 'alcohol-proof', I did not find big changes with alcohols of any common type!  My suspicions are that some dyes may be at work here too.  Again, other things besides MTBE are suspected by me of causing the interior changes.

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, with the contaminants that such solvents can bring with them....and those gasoline's that have, perhaps, alcohol and/or MTBE, or similar, might be affected MORE.

The Bing Independent Float 'kit':::

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 it is the SAME needle, for BOTH.

 The Kit float level is somewhat difficult to initially adjust, having TWO flimsy brass arms.  The arms contact the floats via small pins on the floats, and if not close to correct alignment, the carburetors can flood.  There is NO provision for an overflow/vent for the float bowl, as in the stock float bowls, and thus, theoretically, it is possible for the bike, especially on the left sidestand, to fill a cylinder with UNcompressable fuel...which can destroy a piston and rod, ETC.  The overflowing fuel might go on the ground from a further up carb body port, and not into the cylinder.  I would not count on this.    However, the separate floats seem to be stable for any type of gasoline's, and MIGHT just last almost forever.  There is an article on this website on the Bing kits....

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.

 For these independent float conversions, here are some adjustment specifications:   
With carburetor upside down the most outward part of the brass hinge unit, the top of its flat area, should be 10.5 mm and parallel to the base.  AND...BOTH of these arms MUST be parallel to each other.  For the old model 55 carburetors this was 8.5 mm.   Once in operation, one could remove a bowl quickly, and the center area to top of the fuel should be very close to 1-5/32".       NOTE that after first installing and adjusting one of these Bing independent float kits, they must be RE-ADUSTED after maybe a dozen hours of riding.  This is because the float needle breaks in, and the effect of fuel on the needle and float.  Quite frankly, I think the BRASS also tends to change a bit, something to do with its hardness and tempering grade I suppose.    It is important that the spring loaded plunger on the float needle be in good condition, and the spring inside it not sacked out, or the mixture will be variable due to changes in the fuel level.  

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.
NOTE!.....when ON the bike, that above adjustment is easier to do by observing the point gas just stops or just starts flowing....that is the parallel point, or, should be.  The part of the arm to look at for the parallel-ness is the BOTTOM of the arm. 
***There is a complete article on this website about those independent float kits, well worth your time to read:

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 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.

More details:

Your stock floats are held into the carburetor by a pin that is knurled on one end.   Pins can wear, although it takes a VERY LONG time...if yours are worn, replace them.   Be sure to push the pin out in the proper direction!!  A magnifying glass may be needed to see the knurled end when still assembled.  The pin MUST be pushed OUT with a tiny drift or even a modified nail AT the NON-knurled end.  When reinstalling that pin, this is not the time to hamfistedly use ViceGrips or Channel-Locks and break the float pin bosses.   You install the NON-knurled end first, of course.  The floats may be  tied to the float needle with an easy to loose very tiny wire clip. That clip is there to ensure the float needle releases from the seat.  It is a PIA to install the stock floats...or the KIT bridge...with that wee tiny wire clip and the float needle.  Just takes practice....see below...

****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 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.

I recommend that the diaphragms be replaced at around 30,000 to 50,000 miles, possibly even 70,000. Some of this variability has to do with atmosphere (smog, etc.) and some with time, some with mileage.  I have no objection if you let the diaphragms go until they fail by getting a hole or tear in them. You usually must remove the slide and diaphragm assembly and stretch the diaphragm a bit with your fingers, holding it up to the light, to see holes and tears; but sometimes they are very obvious without the removal and stretching.  You can purchase the individual parts if you need or want to.  Diaphragms seem to hold up rather well over time, so I cannot give a replacement period just for time alone. The type of components in your gasoline also seem to have some effect on their longevity. 

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!

32 mm kits from BMW are 13-11-1-258-051
40 mm kits from BMW are 13-11-1-336-902

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.  

There are a number of rubber O-rings used in the Bing CV carburetors.  All should come with the rebuild kit (5 O-rings).
These are BMW part numbers:
13-11-1-257-739   Used at the throttle shaft, 6 mm x 2 mm and rather thickish.
13-11-1-257-819   Used at the enrichener shaft, 5 x 1.5 mm and rather thinnish.
13-11-1-257-812   Used at the main jet assembly, 8 x 1.5 mm.
13-11-1-254-735   Used at both the idle adjustment screw and on the idle jet, 3 x 1.75 mm

The screws for the carburetor top cover are M5 x 12 oval head

Except for the /5 models, lighter carburetor springs are available....they are not the same for 32 and 40 mm carburetors. Check with your dealership; or, Ted Porter's Beemershop in California.
There is a type 606 for the 32 mm carburetors that have 3 digit model numbers; a type 908 for the earlier 2 digit 32 mm types, and a type 312 for the 40 mm carbs.

There have been some problems with the R45, R65, and POSSIBLY some of the larger engines, from 1979 or so, for a year or three after that time.  The information from the factory on this problem is sketchy.  The problem is poor throttle response of various types, during initial starting and riding off, during quite cold temperatures.  Basically, the enrichment device in the carburetors is not rich enough.   BMW changed the enrichener disc (that disc with the 'funny' holes) by, essentially, enlarging some.  NO change in part number was used.  I have the bulletin on it, which, in essence, says to use a new disc, or, modify your disc, by drilling it with specific sized drills, and exactly which/where.  I have not posted the SI (are two) on this website, because there are other more likely possibilities for cold starting/running (until the engine has been running a few minutes), such as clogged bowl jet, etc....and, the fact that almost no one rides in such extreme weather, and is not likely to be bothered by a seemingly somewhat slower warm-up period.    I can supply the SI.

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!

BMW supplies a screwdriver 71-11-1-103-086  in the on-bike tool kit.    Phillips and standard ends, reversible.  The 'Phillips' end is NOT a PosiDrive nor is it a Reed & Prince tip.  There are better choices, and stronger, longer lasting, but it is not always easy to find a screwdriver that is small, and has both phillips and slot ends, and fits your tools bag for the on-bike kit.  Some folks purchase one of the SnapOn types, with assorted hardened magnetic tips that fit inside the handle.  If you have the room and budget, the Snap-On is a QUALITY tool, that NEVER wears out the tips.  Be sure you have the proper size tips...many come only with a relatively narrow single blade size tip.  The proper Phillips size is #2.   

BMW carb top " phillips" screws are not always really Phillips screws, they just look that way at a quick first glance. They could be Phillips, OR could be 'Pozi' type.   Someone might even have changed them to allen head types.    The ancient aircraft tip screwdriver called Reed & Prince works relatively nicely on the PoziDriv, of course, does the real Pozi-Drive.   The PoziDriv tip is EXCELLENT for REMOVING the phillips type, if the Phillips is way tight.   Generally install a real Phillips type with a Phillips screwdriver, but the other types of screwdrivers DO work better.   If the screws are frozen, you can try a variety of ideas.  The Phillips type of screw was DESIGNED so the TOOL will SLIP after a certain torque is reached.  This is why removing a stuck Phillips screw is so annoying.  Methods of adding friction for easier removal includes valve grinding compound for a better grip.   For egregious instances, I use a metal block underneath and an Impakt Driver with the PROPER TIP.   Tips for interchangeable-tip type tools are available from a variety of sources, including Snap-On, and the PosiDrive tip IS available.    Some have installed Allen head screws at the carburetor tops.  They are OK, but don't over-tighten, as many of these have a very small allen and can round-out more easily.     Some early carburetors had common slot screws.   BMW and Bing may be, and have, shipped EITHER PosiDrive or Phillips sure that your 'screwdriver' fits them.    Remove the screws one at a time, coat the threads...and under head taper...with antiseize....and replace the screws without too much torque; will appreciate these hints much later on.  BMW's red plastic-handled screwdriver that is in the BMW on-bike tool kit, the one with the reversible insert, probably Heyco Germany brand, is NOT NECESSARILY THE CORRECT TOOL for the carburetor tops....this tool is a common Phillips, and not a good one.     The PosiDrive screws generally have some radiating lines to indicate they are not Phillips type.   Note, again, that the Pozi type screwdriver will usually work well on phillips screws.
 Here are photos of the Posi-Drive screw, and the screwdriver tip.  Note the differences from a Phillips....the nearly flat bottom in the threads and the corresponding flat top of the screwdriver; note also the angles and the extra (lesser) 'splines' in-between the major splines.

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, VERY careful that that the proper end fits into the throat, and that the needle does not catch the edge of the 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 rattling noises.

Since wrongly assembling and using force with the slide, needle, and central jet, can damage the carburetor parts badly, I will get into this a second time, a bit differently:
    When you install the main jet, and the parts associated directly above it, it is best NOT to install these parts after, BUT BEFORE you install the slide/needle/diaphragm assembly. Failure to follow this advice can lead to bending the slide needle, you can cause a real hang-up inside, which is hidden from view, and further tightening of the jet assembly using a 10mm wrench can cause you to, in the worst case, split the carburetor boss. This is nasty to fix, most folks just replace the carburetor, or, the body of it. Some do an epoxy job, which MAY or MAY NOT work. Sometimes a sleeve is made and installed, perhaps epoxied also. A new carburetor body is REALLY expensive ...unless you find a cheap wrecked bike to remove it from.  Old hands at working with Bing CV carbs install any way they want to, as they know the feel, do it with fingers initially, and also have their other hand's finger moving the slide needle at the same time, typically lifting the slide fully up.  This WILL work well...and is OK for you to do, just be gentle and watch what you are doing.

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 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 CAN fit.

When one does a mini field-overhaul on a Bing CV carburetor, it is usually not necessary to totally disassemble the carburetor, removing every jet, every O-ring, the enrichener parts, etc.  Normally, one really needs only to replace the diaphragm, float, and float needle and spray the passageways a few times with a good cleaner.   If you removed the idle mixture screw, replace its O-ring, slightly coating it with silicone grease.   At some goodly mileage (Bing says 25K, I say 60K), one should replace the slide needle and needle jet. The reason to replace these is that the needle is designed to vibrate freely, and the two wear each other and change size, the result of which is a richer midrange.  Yes, cheapskates can lower the slide needle one notch to sort-of compensate, but even with very high mileage, this is usually way too much.     Some late model slide needles were aluminum...and the GROOVE wears very fast....they are to be replaced as soon as this is noticed.

HINT:  When installing O-rings, put some common electrical tape over the sharp threads, and use a tiny amount of silicon grease to ease the O-ring into its groove.  Remove the tape afterwards.

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.

Removing the idle mixture screw and spraying all the idle passageways with that very strong Berryman product is a good idea.  Spray three times, waiting a bit each time.  Use plain clear silicone grease, or Dielectric Grease, from your autoparts store... LIGHTLY on anything brass that screws into anything (antiseize is OK), and silicone grease for any rubber O-ring.   Use of silicone grease will tend to protect the O-rings from being damaged when installed, as well as greatly lengthening their life, and making things turn smoother.    DO keep in mind that there are some VERY SMALL holes in certain passageways and jets, and you do NOT want grease clogging them!

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 without. 

Some carburetors have the diaphragm held in differently. Be careful expanding any plastic rings/clips, they can crack. A tad of heat from a hair dryer, on the plastic retainer, or in very hot water, is helpful.  

NEVER clean jets with tiny drills, etc.  There is a danger here that you might increase its size.   It is probably OK to clear a jet with a very thin wire, but be careful.  Typically a wire is not needed, if spray solvent is left in place a few moments, and then re-sprayed.   

ENRICHENERS...yes, a whole choking section on this subject:
Introduction:   This section, 'enricheners' may seem quite complicated at first, it is not, really.
If you take a carburetor apart, you need to be able to assemble it in the correct positioning
of the parts.  That is usually actually very simple.  HOWEVER, some carburetors were MISMARKED
by the Bing factory.  ALL will be explained in this section.  Read it through, then repeat, and
LOOK at YOUR carburetor parts.

A cleaning and VERY LIGHT silicone spray or silicone grease lubing will make its operation smoother.   If the rotating disc, which has holes for jetting, gets plugged (unusual unless you use grease), the enrichener won't work correctly. 

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.  Your bike could ALREADY have them assembled wrongly.    The enricheners be assembled correctly for the 'choke' to operate correctly; the FLOAT BOWL, the corner jet in the well must be clean and UNclogged.
There are two very tiny pipes that must be good, and UNSPLIT, one comes down into the enrichener well of the bowl, the other is in the middle of the bowl, and vents to the underside of the bowl.  Once in awhile water collects in the bowl, freezes, and these teeny pipes split.

Carburetor enrichener parts orientation....
The left side photo, below, shows a dot-dimple on the enrichener shaft, which, if correctly marked and installed, points to the cable-fastening end of the lever. Later model carburetors have two slightly different levers plates, with a notched slot for the cable, & hole for the cable barrel. I have a photo of them a bit further down.   It is possible that some shafts have the DIMPLE, as in the left photo, REVERSED by mistake, during assembly of the disc/shaft.    This can happen for the right or the left carburetor.  By using the views of the inside of the assembly, you can be sure your carburetors are correctly assembled, even if mis-marked by the Bing factory.

NOTE! is possible for the SHAFT to be wrongly inserted into the disc.  The disc on the shaft is spring loaded.  This is particularly so on the models with the disc type, that, pressured lightly with your fingers, moves on the shaft. Remove the nut, which will allow the choke lever(s) parts to be removed, noting how the lever parts were attached. If you assemble them wrongly, the cable barrel will not fit correctly!!!  See a bit further down the page for a more detailed explanation.

Below two photos:  one on RIGHT has shaft market R
this is from a 1978 Airhead RIGHT carburetor.
Early carburetors have the number of tiny jet holes
and the elliptical-tail slot different, with some
holes missing.  There are at least two styles of those.
Although it would be nice to have the dimple, see the
left photo below, such that it
really does point to the cable barrel as designed, it really
makes no difference, so long as the cover with its parts
fits the carburetor in the correct position. 
That position, for the RIGHT-SIDE carburetor, is shown in the
right photo of the two photos below.  If you are more
curious, NOTE where the elliptical hole, and also the small
jet holes align to the body of the carburetor, as you
start to place this enrichener cover/disc/shaft assembly onto
the carburetor.  There are body passageways they must work
with....but you might get confused, trying to figure it out.
The lever shown in the left photo is the ONE-PIECE type
used on the very early carburetors. 

If you were to look at a LEFT carburetor disc and shaft (instead
of the RIGHT, as below), you would see the tail of the elliptical
hole pointing the other direction.
NOTE...the right photo should NOT be construed to have its
shaft/lever in the position of the left photo.


Photos of the enrichener with the lever in the two extremes of positioning are a bit below.

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 right photo.   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 clean/clear!   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.

Besides the photos, above, and below, here is a TEXT explanation, for both left and right carburetors:

If you were to have the LEFT carburetor enrichener unit off the carburetor, and put it in front of you, upside down...that 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 or wrongly stamped! the factory!

Later model Bing CV carburetors have two-piece cable levers. It is possible to WRONGLY install the two metal pieces. 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 barrel  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.
NOTE that the fuel bowl gasket MUST BE IN GOOD CONDITION for the PROPER operation of the enrichener.  The reason for this is complex, but a simple explanation concerns the tiny diameter pipe that comes down from the enrichener circuit in the carburetor top body, and dips into the enrichener fuel well in the bowl.  That tiny pipe has one or two holes in it ABOVE the pipe lower open-end.  Vacuum, during the starting sequence with enrichener (CHOKE as marked on the bars assembly) ON, causes fuel to rise in the enrichener well in the bowl to a higher level than in the rest of the bowl, creating even more richness than might otherwise be possible.  If the gasket is leaking air, the maximum enrichment will be LESS.  
Note too, that due to the over-all enrichener design, the amount of enrichener to be used, and whether or not you need a bit of throttle opening during cranking/starting, and after just starting, can be rather variable.  
Most  owners booklets say to not open the throttle, as it defeats the enrichener, and this is really a vast simplification and not really all that true.  You very well MAY need some throttle opening during starting, and this depends a lot on the particular motorcycle tuning and temperature, fuel volatility, etc.

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.

NOTE!!!!   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.

Very early Bing CV carburetors have pressed-in float bowl enrichener jets, not screwed-in.

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.

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.

***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!, 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 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 later enrichener (choke) control and all throttle controls on all the carburetors, each have an outside return spring.  The springs are not the same.  The old style carburetors had the enrichener (choke) lever on the aircleaner housing, and springs were not needed as the cable inners were very stiff single strand of steel wire.  The lever assembly at the snail housing can be disassembled and cleaned and lubed, as they tend to get stiff with age.  It may be necessary to adjust a size of a thin shim to allow smooth you do not want the nut loose.  Sometimes that area takes some fiddling with.

 THREE styles of throttle return springs were used.  The earliest type fit AROUND the throttle cable center.  It was not a good type, and the throttle was pretty stiff.    Later types had the springs attached to the throttle lever and a carburetor boss projection with a tiny hole.   If a spring is stretched or misshapen, replace it.  On the old style carburetors, that stiff spring must not rub against the carburetor, if it does, change the inner fit to outer, where the cable barrel joins the lever.   Far nicer throttle feel can be had by modifying the oldest style CV carburetors so that the spring is NOT wrapped around the throttle cable outer sheath.  Not a simple thing.

Hate to repeat myself, but....If you remove any jets, etc., that have O-rings, you SHOULD replace those O-rings. I prefer to put a faint smear of silicon (or even petroleum) grease on the O-rings when assembling to help avoid cutting them (the tape over threads helps as does room temperature or a bit above, as opposed to freezing weather).  Also I put a faint amount of silicone grease on the threads when assembling.

The one jet ASSEMBLY that I always recommend be removed, to clean that area in the carburetor is, in order from the bottom (for your future reference):  the central main jet; the washer above that (do not substitute the type of washer, don't leave it out); the so-called mixing tube (brass part, with O-ring and outside threads, with 10mm hex sides) above that; the needle jet above that; and the atomizer above that. This information is for those who have removed things, have not 'seen' the direction of assembly, or have forgotten the direction of the parts. If your carburetor has the acceleration pump assembly, it is slightly different looking.  Note previous cautions about screwing in the central jet, not to trap and crush the needle, and note also that the atomizer (the top most part) fits only one way, and it will then, properly, stick upwards INTO the throat.

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.

You MUST assemble the central jet assembly parts in the correct order.  Do not over-tighten.  If the slide/needle is already installed in the top of the carburetor, be cautious about not letting the needle hang up on the central jet 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 later.

Cleaning the idle system...jet, holes, important, and the Berryman's works well, if allowed to work awhile.  DON'T bugger the end of the idle jet with a poorly fitting screwdriver.   Rarely the idle jet has been known to freeze in its threads.  If you break off half of the screwdriver slot end, drill it carefully and use something like an EZ-out.  I will use heat on the surrounding alloy, to try to enable removing, before going to drilling.  

When 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!

Don't fail to spray clean the jet in the 'well' of the bowl, and the overflow tube too.  I've sometimes had to poke around at that jet with a piece of wire to clean it.

The left and right carburetor bowls are NOT the same.   The corner well, containing the jet at the bottom fits the tiny diameter tube projecting downward from the carburetor body.   This is the enrichener source.

I always clean the various metal parts with the mentioned Berryman's brand of carburetor/choke cleaner spray. For a major overhaul, take everything apart and use a professional cleaning tank if you have one available.   There are many types of spray cleaners available at your local auto parts store. Some are NOT very good. A good one will instantly dissolve a fair portion of the brown stain deposits if you have some, on the carburetor outsides, sometimes a cotton swab will help. I prefer the spray by Berryman, called B-12 Chemtool, Carburetor & Choke Cleaner. This is nasty stuff.  Hopefully Government regulations will allow it to continue to have the strong formula.   Use outdoors, or with your garage door open!  It is also very good in just spraying off the stains on the carburetor outsides now and then.  Common so-called 'brake cleaners' are AWFULLY BAD at cleaning carburetors properly. 

Be sure the main jets and needle jets have the proper and same size number on them, left and right. If you have removed the idle pilot jet, be sure the numbers match. 

Every once in awhile, someone asks about removing, or changing the setting of the slide needles.  Even when there is a definite reason, such as gross modifications to the exhaust system, or the carbs are U.S. specification and you want to richen to the British specification by moving the needle position; changing the needle position by one notch is often WAY too much, and the better method is to change the needle jet to the next size. In many instances the British-shipped carburetors have both needle size and needle jet size BOTH changed.  This is almost always the better approach.  Another approach is to ASK BING!...they are usually quite helpful...and their carburetor parts and service booklet is worth the $.

 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.

The rubber 'hose' adaptors from the carburetor to the cylinder heads are sometimes found to be leaking.  This is usually proven by spraying them with any spray cleaner such as 'brake cleaner' at idle speed...should be no idle speed change. Keep the screws on the band-clamps tight.   This is the perfect time to spray the throttle shafts too.   NO idle speed change at all is proper and acceptable.

Fairly often I see carburetor top stains where they join the body of the carburetor. The tell-tale sign is a brown (usually) stain around the diaphragm joint interface, caused by some tiny gasoline weepage.  I was never bothered by this, as the 'problem' is sporadic and minuscule.  However, Oak sent me (in 1984!!) a bulletin he made up describing this situation as not necessarily being caused by the lack of the diaphragm acting as a seal, but rather that the compression of that diaphragm was insufficient for a COMPLETE sealing. He recommended removing the carburetor and flat sanding the carburetor top itself, with 220 grit wet type paper, kept wet with water, figure eights, carefully, until the groove, which he said was 0.155 to 0.156 inch deep in the troublesome carbs, is reduced by about .007 inch. He said to shoot for a final depth of about 0.147 to 0.150. Remove all grit. I have done this to several carburetors, and it DOES stop the staining. Frankly, few of you have the gauges to measure this, so you could try just a few figure eights. TEN is appropriate, medium pressure. Do them EVENLY, with even LIGHT pressure.  Once the fresh sanded surfaces are evenly fresh all the way around, that is likely enough.  Do not overdo this.  Clean and reassemble.

Some carburetors (not the flat top ones) have had leaky steel plugs on the domes...that shiny center area. You can easily test the plugs for leaks when the domes are off for servicing the carburetors. DO NOT allow any will act like a torn diaphragm. They can be crimped or epoxied. I prefer crimping with a tiny tip punch and then epoxying.  Some folks have used a toothpick and aluminum paint.   If your plug has a letter C stamped into it, do not cover it up, it means identifies an early modification in the /5 era.    There is a BMW Roundel that can be epoxied to the top of the carburetors (they fit the small top ones, also the flat top ones, which can also use much larger ones too). 

See article on this website, for a huge list of Roundels, including exactly which fit nicely the small tops.  When cleaning the area for epoxy or aluminum paint, etc., it is very difficult to get sandpaper into the corner.  I use a dental pick or awl.

HARD STARTING, maybe ONE carb does not work well initially, then works OK after engine running & throttle opened:

 If starting is still poor, it may be that the slides are not returning fully.  Older advice was to check for that and  fix by installing springs 13-11-1-335-324 above the slides on 40 mm carbs, and 13-11-1-338-134 on 32 mm carbs.  This did not apply to the flat top carbs.

Tom Cutter once said that this modification, installing a longer and softer spring on the slide, will smooth the idle transition at the 1/8th to 1/2 throttle movement.  Tom said that the shorter, earlier spring, used on the 40 mm Bing CV carbs, was 13-11-1-335-324.    He installs the longer softer spring 13-11-1-338-134, as used on the 1988-1995 R100 models using the 32 mm carbs (these springs, per Tom, are used on the EURO R100GS 40 mm carbs).
I have my own input on this, besides the earlier paragraph.   Some folks DO prefer the more abrupt throttle action of the stiffer spring, which is about 115 mm long and has about 30 coils.  The softer springs are about 120 mm long and have about 20 coils.

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:


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.

ON all models, and the Independent float KITS too;....the floats are adjusted by bending the tab that the float needle (and wire clip, if used) attach to. I have found a TINY screwdriver does this OK, and seems to work better than unwieldy long nose pliers.  Do one carburetor at a time. BE GENTLE AND CAREFUL!! it evenly too...not just at one edge, which bends the tang on an angle you don't want.  In other words, keep the tang flat and square.    After making a small change... turn gas on, lift float gently and SLOWLY with protectively gloved finger, until the gas flow JUST stops. At THAT point where the gasoline JUST stops flowing, the top of the stock floats are to be parallel to the lower body of the carburetor. I allow as much as .020 inch below, maximum. I have done some fine-tuning by playing with the float level, I suggest you do NOT.  Some folks find it easier to lift the float until the gas stops flowing, and then very very gently lower it until the gas JUST flows.  This MAY well be the preferred method, as it eliminates the effect of the spring loaded lower tip on the float needle and eliminates any play in the pin and hinge holding the floats in the carburetor.   For the KITS, the adjustment is the same, but the measured distance is .412" from either lower arm edge to the body.

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 mileage. 

Major tuning/adjusting the carburetors is not part of this article.

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


to 12-07-2002:  mostly clarifications.
Through 12-09-2002:   add area for upcoming float testing; added references to Bing CV Carburetors-2,
                                  many clarifications and emphasis items.    This version was not to be released to
                                  the website, pending more additions.
01-30-2003:  Updated many places, decided to release to the website even though float testing has not
                    quite begun yet.    Added a complete section on the enrichener orientations.
03-30-2003:  extensive information on Bing dual independent floats added.
06-21-2003:  Add NOTE and HINT on band clamps.
07-13-2003:  Add all information on float testing done; clarify many areas.
07-14-2003:  Edit for clarity
07-20-2003:  Add note on float/float pin clips not being used on some models
07-22-2003:  Expand about the two types of retaining for the slide needles
09-30-2003:  add top of article notes on Gary L. Smith's article
09-30-2004:  add url for Bing's chart of component description and numbers
02-15-2005:  minor updates.
02-18-2005:  hyperlink to bingindependent.htm
10/18/2005:  general updating
11/30/2005:  update enrichener/choke information
04/23/2006:  add emphasis note on screwdrivers for the Bing tops.  04/24, modify that again
05/11/2006:  Bing diaphragm caution note
08/24/2006:  Add photos of enrichener parts/orientation (left parts)
03/04/2007:   more information on the Stromberg diaphragms and cautions on their use.
05/03/2007:  Fix hyperlink to; and generally update the entire article
07/06/2008:  replace enrichener photos with better ones.
04/19/2010:  Expand description of the enrichener parts assembly and alignment, regarding the dimple,
                    jet disc, etc.; later in evening, add more comments, so is no mistake about how the
                    enricheners all assemble.
04/25/2010:  Add photos, Posi-Drive screws and screwdriver tip

04/26/2010:  Twice today go through the entire article, simplifying, changing to more legible & less
                    numbers of fonts & colors. Especially, fix the Enrichener section, making clarifications,
                    adding photos, etc.  Final version release 3:12 PM PCST
02/16/2011:  Added another view of enrichener cap assembly...with commentary.

05/15/2011:  Clarify the enrichener a tad more, and remove one photo that was confusing.
08/15/2011:  Revise diaphragm and Stromberg information
05/14/2012:  add butterfly photos
05/17/2012:  Clarify information on the slide springs.

10/14/2012:  QR code and google update code
11/06/2012:  Expand Bing independent adjustment area
10/09/2013:  Add more to information on float needle and seat.
07/15/2015:  Update a few areas for increased understanding/clarity.

© copyright, 2014, R. Fleischer


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