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Bing Carburetor FLOATS

As on BMW Airhead Motorcycles

Copyright 2015, R. Fleischer

Float needles:
Bing carburetors FLOAT NEEDLES, whether the pure slide type carburetor, or the CV type carburetor, both as used on BMW Airhead motorcycles, come in several varieties.  In general, TWO versions will fit all the Airheads carburetors.    Very early carburetors had a solid metal needle.  That needle was available in more than one 'style', but for all, there was NO rubber (or, Viton) tip.  The other type of needle, that most of you Airhead owners have, is similar to the photograph, below.  The needle shown in this photograph has a spring loaded plunger with a hole in it, with the easy-to-lose wire clip, and RED tip material.  GRAY-BLACK tipped material will also be seen.  I suggest purchasing the stock type needles from your BMW parts supplier, and not Bing themselves.

The all-metal needle used on early models is a different size, and will not properly fit later carburetors, and, vice-versa.   Be sure to get the correct needle.  If you want to install a Viton-tipped needle in a carburetor that used the Bing all-metal needle, you can, per Bud Provin (, who says to use the very common float needle used on many old Amal carburetors, as used on old British bikes.  The part can be found on a simple internet search, for  float needle 622/197;  or, as    013, 622/197.


This article INCLUDES reports of testing that went on for many years, specifically from 2003 to 2015.

Bing stock float, a 1-piece assembly.  Here, this float is OLD, discolored, light to medium brownish.


ALL of the Bing carburetors used on all of the Airheads, which means Bing 1/26 (model 53, not a CV), 64, and 94, with STOCK floats, have a specification for brand-new floats of 10 grams.  After they have been in use they tend to get heavier.  About 13.5 grams is near the maximum allowable. If they get heavy enough, the carburetor float bowl fuel level will get high enough to overflow onto your boots.   This has nothing to do with the problem of dirt getting into the floats needle & needle seat, which prevents that 'valve' from shutting off as fuel level rises to the adjusted value.  While you CAN adjust the floats to compensate for float weight increases, & you may be able to do this several times; eventually, you will have to replace the floats.  MY recommendation is to NOT adjust floats to compensate for their weight increase, but to replace them, at least if the depth of color is as in the above photo. It is possible for floats to be overly heavy and NOT badly discolored! Replace if the get too heavy, even if not heavily discolored.  The BEST test is place the float in a container of gasoline, so see how much of it floats above the surface; this is a better test than weighing the floats, although that can also be done....see information in this article.

The floats, my extensive testing. Information on failures. Alcohol in fuels, etc. :

The stock dual 'one-piece' plastic float assembly, as in the photo at the top of this article, 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 be floated). Once it deteriorates & begins to sink, your mileage will get worse & worse, eventually perhaps with fuel flowing onto your foot.  You can adjust for this only so much by adjusting the metal tab.  I advise NOT doing that.

Floats are not consistent in how they fail.  That MAY be due to the types of gasoline they are used with.   New floats weigh about 10 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 age.   Once they are removed from gasoline & very thoroughly internally dried (which can take a lot of time), they may lighten considerably, & then not gain much weight if again put back into gasoline; at least for a month or two period of time after drying.

The reason for the floats failing is not well understood. It SEEMS to be a change in weight, but also, perhaps, a shift in mass (BUT the OUTSIDE dimensions do NOT hardly change).  The floats mostly fail by increasing their weight.   It is now my belief that floats get heavier by absorbing 'strange' components in our gasoline's.  It is my belief that ALCOHOL, specifically Ethanol, is NOT THE CULPRIT.  Gasoline's contain many compounds, some for anti-corrosion, some for helping to keep clean the underside of valves & other areas; some to ensure that other components stay dissolved (these are usually called CO-SOLVENTS);.....ETC.

The floating test is the "only perfect test" for determining if a carburetor float is usable.
   This simple test will be explained in this article. However, you can get a pretty decent idea about the floats by removing the float bowl and checking the fuel level.

Information from truly 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 & CV Bing carburetors, some were very old indeed; others not very old at all.  Testing took quite a few months.  I actually did some tests for YEARS, concluding only in 2015.  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 & then put them in sealed glass containers with various fluids, & let them soak at least a month; 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 common solvents would 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, Refiners add them to ALLOW other components to MIX with the gasoline, that might not mix & stay mixed (dissolved) by themselves.   Yes, they do this to even allow SOME 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 containing fuels (and several other additives) will USUALLY result in a LEANER burning condition, generally meaning higher engine temperatures, & if severe, can lead to burning up pistons, problems with the valves, & even engine seizure.    While it is true that alcohol has a higher octane equivalency, using alcohol requires, for the BEST combustion, more VOLUME of alcohol, hence LOWER fuel mileage.   In order to maintain more consistent burning, one really should change one's jetting (needle clip setting up one notch at very worst case, usually just a needle JET change, and possibly 5 points or bit more on the main jet) if alcohol fuels were used all the time, & the fuels were reasonably consistent in formula.  This would REDUCE gas mileage slightly but driveability & cooling would be enhanced.    For Fuel Injection vehicles, nothing need be done, since they have compensating devices, although alcohol-laced fuels MIGHT deteriorate earlier FI vehicles rubber, etc., parts.

Use of alcohol-laced fuels should absolutely NOT be used in PREMIX type of 2-stroke engines, as the alcohol & water can separate out of the oil & 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, & Airheads from the 1980's, especially those exported to the U.S. are like that; you might have WORSE driveability problems....or...some overheating. Testing for alcohol can be done rather simply, but it is a PIA to do at every fillup, & this type of testing (mixing in a test tube, with a known amount of water, shake very vigorously, and WAIT to 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 SOMEWHAT to other States, although California has made use of MTBE illegal in every part of the State due to its disastrous effects, if spilled, on underground water supplies. 

Testing for alcohol content is now not all that informative unless you suspect a special problem with, perhaps excessive alcohol, etc....BECAUSE: Alcohol-laced (Ethanol, or gas-o-hol) fuel is now STANDARD in the USA.  It is typically difficult to find alcohol-free fuel, and when you do, it is $$.  It is a political football.  If you have been reading & thinking here, you may wonder about the reduction in smog/pollution emissions, with 10% ethanol-laced fuel, in light of MORE fuel having to be used per mile.  Well, it is nearly a total wash, that is, equivalency.   Thus, putting ethanol into fuels, except for MAYBE big dense cities that have particular smog problems, is a total waste of resources; and, might be a waste in big dense cities too. The major benefit of ethanol in our fuel is to enrich certain very large farmers (of, usually, corn) and such as huge industrial businesses such as Archer-Daniels-Midland....and, of course, some politicians wallets.  That use of corn, yes, even the special type of corn used for making alcohol, results in higher feed prices for chickens, turkeys, beef, ETC....reflected in cereal prices too.

Some States have required labeling the pumps, some do, or did, 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 alcohol) and methanol, sometimes called wood alcohol since that was one old 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 VERY hard on rubber & brass & plastic parts. Bad for the hoses too. THAT covers just about everything in your Airhead's carburetors but the steel pin, needle & the diaphragm (might affect those too). All 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 gas-o-hol will raise the octane, but leans the mixture in the bike, which is why most fuel injection cars can get away with using it (at a cost in mileage & some power), but many older carbureted vehicles may not like it. The better of the alcohols is isopropyl, it tends not to separate out & 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.   BMW has issued quite a few Service Information bulletins to its dealerships warning about the use of alcohol-laced fuels, including warranty disclaimers.

Generally, with the use of a product like Stabil (etc), something less than one year is the best one can hope for in storing your motorcycle with gasoline left in the system.  A side note is that it is ENTIRELY possible for gasoline to be made that stores for MANY YEARS.  Aircraft gasoline is of that quality.  (this is not a recommendation to use it, as it has other problems if used in our bikes).  The best thing to do if storing your bike for the Winter, or longer, is to clean and then dry out the system, including the tank.  Cleaning the fuel tank thoroughly should already be on your scheduled maintenance list!...a YEARLY chore. 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, 'rubber' hoses, and, of course, the carburetors. It tends to gum up and leave hard surface deposits during deterioration.  It also tends to cause the alcohol (etc) to separate from the gasoline, if there are nighttime temperature and humidity changes strong enough to produce dew condensation on things....which also means dew (water) collects INSIDE the tank, and the water droplets flow down the inside into the liquid...and rest at the bottom...eating away at your tank!   Note that what is happening is that the moisture percentage gets large enough that the special co-solvents cannot handle it, and things begin to separate out, and the water sinks (into your tank seams, etc.).

A product often called 'dry gas' is sold to car owners in wintry States, as it, an alcohol...usually methanol or isopropyl, mixes with any collected water at the bottom of the tank & in fuel lines, enabling the water to be 'burned' to speak.  Adding that product MIGHT increase the alcohol & water content of the gasoline to a critical level...causing a separation process...& water & 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.  USUALLY that does not happen by just adding 'dry gas' products.

Types of liquids I tested:


Isopropyl alcohol, high % (91) as well as mixed with water (as in home type).

Ethanol....medium %, as well as 154 and 191 proof; plus, above with varying water content as well as chemically dry (anhydrous).

Toluol (toluene).

California MTBE gasoline (no longer available for testing now).

Known standardized Chevron 91 octane fuel.

California reformulated fuel, which has alcohol added and is known as Gasohol.

Leaded fuel (yes, TEL added fuel, as with aircraft fuels)

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, & a few other things.


RESULTS OF MY ABOVE TESTING (including work ending in 2015:
1. Weight change (weight is in 'grains'; because I used a sensitive gunpowder scale; 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, and gasoline's, 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.

Note: some folks sent me information on weights that I could not duplicate. I was rather suspicious, & then I made an interesting discovery. If a float was never dried out thoroughly from first being put into service, UNTIL removed & replaced, & then sent to me, then the weight might tend more to agree with information I was given, as that weight was 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, & 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 & 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 & kept in gasoline (except perhaps for very short periods allowable without gasoline...such as carb bowls off, perhaps for a day's overhaul), does change internally; the internal change is permanent...or if not, it takes a VERY long time for the change to revert in any substantial amount.  

2.  Tests were done to determine if there was a shift in the concentration of mass.  This WAS found to be so, BUT 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.

3. Change in dimensions: of each float assembly, both sides were measured for width & 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, & become slowly more impervious, whilst the nastier fuel components get inside & do their damage on the float inner portion.  Later work, ending in year 2015, tended to strongly show that the float weight increases are caused by absorption of some sort of additives in the gasoline, that were NOT any of the solvents I tested, & I believe are not any sort of solvents at all, but are various metallic or otherwise additives that can add their weight, even if in miniscule quantities, to the float material itself, and are accumulative.  In other words, SOMETHING discolors the floats & adds weight, & some things may & do add weight to the INternals of the floats, & those substances may not be the same that discolor the outsides.  NO formal laboratory tests were run, due to cost; although I thought I had a spectroscopic analysis lab lined-up for the work at one time for free.

4. INternal discoloration was NOT noted on some, but the worst were ALWAYS discolored.  Almost no truly bad float-sinking reports by owners were still white on the outside (although some were INternally a bit darker).

5. ONE SPECIAL THING WAS NOTED!! As the floats became worse....that is, they tended to sink in gasoline more & more, this means they became heavier.....the INside of the floats tended to turn into a somewhat MUSHY & 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, & 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, & generally INcreased the internal mass weight.   Mushiness and granularity were not the only changes 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 strongly that something, ...perhaps something in gasoline I did not test for (dyes, metallic compounds, etc)....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 more 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 and various special combustion cleaning additives may be the cause.  I also believe that metallic and non-metallic compounds imbed themselves into the OUTER surface.

6.  I did an interesting test in late Summer and Autumn of 2005.  This was 10 years before I stopped all testing.  I obtained a float & I measured only weight, & 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 pecuniary 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.

Conclusion:  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 & additive compounds in today's common gasoline's.  The shift is in weight, mass (which tends to shift more on the lower leading portion of the float, so the float weight change is amplified in carburetor effects.  The only answer is to replace the floats when needed; or, go to the problematic Bing dual-independent kits.

One final word:
I failed to do one test, from the beginning, because I did not think of it.   I should have tested a brand-new float for years, weighing it now and then, with it ONLY in 100 Low Lead Aviation fuel.


09/12/2015:  New article, which comes mostly from old bingcv.htm article, previously 3, now 3A.  There is added information in this version.
01/08/2016:  Meta-codes revised. Font increased. Article clarifications.  Narrow the article, to left.
05/09/2016:  Final update to meta-codes and scripts, layout changes, interpretations and additional clarity.
04/23/2017:  Improve information on Bing float needles.

Copyright 2015, R. Fleischer

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Last check/edit : Sunday, April 23, 2017