Bing Dual-Independent Float Kits
As used on BMW Airheads Motorcycles

© Copyright, 2011, R. Fleischer

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"My Airhead motorcycle came with the twin independent float conversion... why do the gurus "hate" them?    I also would like to know what IS the proper procedure for adjusting the float levels on carbs with this conversion, assuming I am going to do it myself ..." (and other inquiries.....)

 I did a major article on these kits on the Airheads LIST a long time ago, including discussing the original engineering behind their development, which Bing would probably prefer I not post.   NOTE that BMW never installed them,... it would hardly have cost them anything...there are several reasons they did not.

Primarily there is the lack of an BOWL "overflow" (really a VENT) that has "guru's" most upset.     All the Bing CV carburetors have an overflow capability at a vent port on the carb body, which is rather high up, and likely will not prevent some flow into the left cylinder if the bike is on the sidestand, and thus there is a danger in starting the engine with a liquid lock for ...busted pistons, bent rod, etc.    With the Bing independent float kits, there is no BOWL vent, which acts somewhat as an overflow.  You can see this by looking at the Bing bowls in the kit, versus your stock one...there is NO vertical tiny pipe in the conversion bowls.

 I have nothing much against use of these Bing Independent Float Kits, or alcohol-proof kits, or whatever Bing Agency in the USA advertises them as.  Just be sure your petcocks work, don't leak internally....and are in the OFF position (horizontal lever position) if using the sidestand.   You will have to monkey with the flimsy slide adjustment a few times, but after that, they settle down and are reliable.  You will still have to replace the float needle now and then, perhaps 30K-60K intervals. 

SO....pay attention to my advice to always turn off your petcocks when the engine is off (Bing ALSO cautions this).  This is particularly important if using the sidestand.   

 The conversion DOES NOT greatly improve throttle feel in tight turns and DOES NOT greatly improve gas mileage, as Bing originally touted.  If you read what Bing originally wrote, they were for transverse mountings, amongst other things, not really like BMW Airheads.  It is my belief that these kits were developed originally for small aerobatic aircraft, and only later Bing decided it could sell many more, at a handsome profit, to motorcyclists.   AND, yes, I have the original Bing engineering bulletins on these kits, from decades ago.   

Of course if the original floats which DO AGE are really bad, and or the float needle bad, things will certainly improve with PROPER installation of these PRICEY kits!...and THOSE are likely the HONEST and TRUE reasons that SOME find improvements with these kits!   

The twin independent floats in these kits seem to last forever in any type of gasoline or time and miles (NOT so the float needle).....but the adjustment brass-looking bridge is thin, flimsy, and is poorly heat treated.  It is possible that this was done on purpose, to be fair about this.  That brass-looking bridge needs to be adjusted properly at first install, and then once or twice more after being in use for awhile. Bing says readjust (implying once) after 5 hours, I say this is not enough, and should be checked again after maybe a month or two, and then maybe at yearly....or even longer, intervals; typically they are fine after they settle down.

NOTE!!!.....The float needles in all the CV carburetors were (very early) a solid metal, and later Viton (or? rubber) tipped, and are now the same part number, no matter if the tip is black, gray, red, etc.   The float needles in the Bing dual-independent kits are the same as the stock types.   Float needles wear out...and allow overflowing with the kit...and if stock floats too.   

Float needles are prone to being damaged by Gasohol.....and it MAY be best NOT to drain the carburetors and let those tipped float needles dry out during Winter storage....as they get irreversibly HARD, and do...or MAY... not seal well when put back into service.   Bing also charges a lot of $$ for them!   I have seen many that DID hold up to being dried out, however.

***NOTE! that BMW dealerships generally charge LESS for Bing carburetor parts than Bing Agency does, but the dealerships may not stock the independent float kit parts (as they are not BMW parts)...although the FLOAT needles are the same).
 

The Details:

One must be careful to avoid mis-adjustment of the bridge....it could then cause rubbing, or uneven, even angular, float operation.   If you mis-adjust the bridge, you can get all sorts of problems, from flooding to mixture problems.    This is NOT a difficult job, just be slow, cautious, careful, and you will do just fine.  ALSO, be cautious about the vertical float pins in the float bowls....those two pins have been known to be bent, and need gentle straightening...otherwise the floats might stick at the bottom (more, later on....).

The big advantage of these kits is that you do not ever (probably) have to replace the floats. That advice does NOT apply to the float needles, of which there were TWO basic types, and the VITON tipped ones have the easy to lose fine wire clip, same as on the stock carburetors, that insures positive float needle operation.   

On the Bing CV carbs, as STOCK, with the die-cast aluminum-looking (probably zinc?) float bowls, there are two round holes, fuel wells, in the forward corners of the float bowls.  ONE is plugged off, with the opposite one for the other carburetor, as there is a left side and a right side bowl.    The one NOT plugged off is a 'well', with a small jet at the bottom.   That jet, on the stock or kit bowls,  SHOULD be checked for not being clogged, if you remove the bowl.  The well is where the main body of the carburetor has a small tube that dips down into the well.  This is where the enrichener gets its fuel.  BTW...the float bowl gasket must be in good condition for this to work properly.

 The Bing "alcohol-proof" kits that have PLASTIC BOWLS (that I have seen so far) do NOT have any corners plugged, but the jet is in only ONE of the wells, just like the stock bowls.  In fact, these Bing kits were furnished with the jet in a baggy, UNinstalled. YOUR newly acquired bike with the kits, already should have the jet properly installed, one would hope, at the correct corner...do check that. Especially check this as Bing shipped kit bowls with NEITHER corner plugged off.   The proper corner FOR THE JET is the one that mates to the DOWNward pipe coming from the carburetor body corner.   If the jet is not properly installed in the Bing Dual Independent kit, the 'choke' (enrichener) will not work correctly.  NOTE that in the plastic bowls I personally have seen, granted not a large quantity, the NON-jetted corner IS drilled for fuel to get into its well from the main bowl.  In the stock metal bowl, a different construction prevents that.  If a dual-independent Bing bowl was installed with the jet not in the proper corner, the bike would start OK, I think.  But,  this would allow a greatly over-rich choke (enrichener) action during the warm-up period.   The jet is there to fill the 'well', so that a very rich initial STARTING mixture is possible....and after approximately 15 seconds of running, the bowl is supplied by the quantity allowed by the JET.    Thus, the jet not in the correct corner could allow some washing down of the cylinder walls with lots of fuel over too many seconds of operation .... not so nice.   Whilst I have not personally seen the PLASTIC "alcohol-proof" bowls with one well plugged off, they could exist, and then, if the bowls were swapped left-right, the bike would be very difficult to start, especially when cold.  So, the thing here is, DO NOT install the wrong bowl at left or right; and, be sure the jet is in the proper corner.  EASY to see which goes where....the carburetor has a very tiny thin diameter pipe, going downwards,,,,,it must go into the JETTED bowl corner.

SOME 'kit' plastic bowls have had microscopic cracks at the corners, leading to weeping. Bing then started selling METAL bowls for the 'kit'.  All of the metal ones that I have personally seen have the jets already mounted in the corner, properly. If you order a bowl, you are going to get the metal one.

SO....Bing has been shipping zinc bowl kits...corner plugged.  DO check that yours are correct....   The Bing kit was, as I have mentioned, LIKELY designed for aerobatic small aircraft, and that is why they have no BOWL vent...and other changes in the bodies were likely done upon installation.  Bing PROBABLY had a lot of money invested in the tooling for these parts, and some smart salesman decided that they could sell the kits to motorcyclists, as they are unaffected by Alcohol, ETC.   LOTS more motorcycles with Bing CV, than aerobatic aircraft being built.  SOME Airheads HAVE noticed fuel mileage increases.  My suspicions are greatly that it was simply due to the kits not having old sinking stock floats; or, maybe a new float needle, or maybe the level is set a bit leaner.   It is very important that owners of these kits understand about turning the petcock(s) OFF (and DO check the petcocks for leaking internally when OFF); and, that the very flimsy, poorly heat-treated brass-looking 'bridge' needs careful adjustment, and then a readjustment after some period of time, then checked once more within a year.  If very carefully adjusted, they seem to work OK.      If the float guide pins are bent, the floats can hang up!   I have also seen some floats with poorly peened tubes in the float itself.

Adjustment:
I will assume the new twin independent floats kit was properly installed.
If the carb is OFF the bike:
      First, turn the carburetor upside down.
Adjust the tab on the bridge piece and the arms themselves, so the arms are dead-parallel to the carburetor base.  Use a very small screwdriver, very carefully, to adjust the tab.     The arms must remain parallel with the carburetor base and the two arms parallel to each other.   When you are finished, it is critical that all these conditions be proper at the same time.

If the carburetor is ON the bike:
 You have to lift the arm assembly very VERY gently with a fingertip, and NOT ..NOT!....allowing the spring loaded plunger in the float needle to be depressed.   Same adjustment(s) are to be done.

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. 

When using the small screwdriver, you bend the tab against the steel bridge retaining pin.   You will see what I mean when you try to figure out how to bend the tab.

Note:  A little known problem with the individual independent floats themselves is that there really is a top and bottom to SOME of them.  Bing ignores this.   Because of the tight fit at the bottom combined with the slight upward slope (and very close to the bowl rod) of the bottom of the 'new' float bowls, the floats CAN, sometimes, 'stick', to the bottom of the bowl.  They can also stick at the bottom if the pin is bent even slightly!! 
Usually this 'potential problem' does not cause a problem due to the motorcycle vibration during operation.

 Install the floats on straight up pins...and also so the center metal pipe area (that is part of the float) is such that the broad-rivet head of that pipe is DOWNWARDS, to the bottom of the bowl.     It is possible to actually 'feel' this float grabbing at the bottom, especially if the rounded larger head area is up (or pin bent), instead of properly down...which raises the floats very slightly off the floor of the float bowl.   I had one bowl that I saw that this was exceptionally poor....so I put the floats in rivet pipe head downward, and a very small and thin washer went over the bowl's rods first.

It is somewhat easier to do adjustments on the workbench, carb upside down.   It is a bit tricky to describe without a sketch....Bing probably still has install instructions for its dual-floats...but...here are some scanned images.   These have all sorts of my scrawlings on them!

I have changed my mind....and think it OK to use these things...as opposed to what I wrote on the below bulletin, back in 1999::

....OK.... pay attention here!:::
If the carb is upside down, bowl and floats off of course, have the float pin to your left, and view this assembly from horizontally, not vertically.  The RIGHT end of the arms (the two arm ends MUST be parallel) have a wider area on the right-most part of those arms.  You could describe it as wider by a small amount.   The UPPER surface of that wider part must be not only be parallel to the carb base body, and both arms even to each other....but the DISTANCE from this upper surface arm part to the carburetor base must be 10.5 mm...which is 0.412 inch.      This covers all the CV carb models used on our airheads...there is a different specification for ONE model of Bing not used on the airheads....it is listed on the sketch above, for model 55 carburetors, where the distance is 8.5 mm.

After some hours of use, reset this bridge if needed.   The bridge will change its adjustment slightly due to its heat treatment (I THINK),....and some settling-in of the tip of the float needle.....and teeny changes in the internal float needle spring parts.   

  NOTE that you WILL have to change the float needle now and then, perhaps at 30,000 mile intervals, and recheck adjustments.     The adjustment of these twin independent float kit units is more tricky and time consuming than the simple adjustment method of the stock floats.

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".    

Revisions:
02/18/2005:  Clarifications and final release
05/22/2005:  Add extensive notes, yellow background
05/24/2005:  add 4 scanned pages, modify descriptions, minor other things
08/24/2005:  Go over article and clarify some details
06/24/2007:  Edit the article for clarity, add more cautions.
01/10/2008:  Rechecked article
04/13/2009:  fix very minor typos and clarified a couple of details
09/13/2009:  Correct typo in ...OK.... pay attention here!::: area, where I had 19.5 mm instead of proper 10.5 mm.
05/17/2011:  slight cleanup.  Still a very messy article!

© Copyright, 2011, R. Fleischer

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