Leaky Bing Carburetors

Bing Carburetors that pee gasoline onto your boot; or,
weep or leak onto the floor of your garage…..
How to do the Bing Dance!
Fuel foaming from vibration, particularly on GS models.
Float needle seat replacement.


© Copyright 2021, R. Fleischer

For float testing in depth: https://bmwmotorcycletech.info/bingcv.htm

For actual fuel level measurements & information on replacing float needle SEATS:

It is important to turn off the petcock(s) when you park your bike, even if you have a late model Airhead that has the fuel-shutoff solenoid valve located on the inside of the cover over the starter motor (many have been removed, but the same caution applies). If you park your bike in a garage where there is a source of gasoline fumes ignition …such as a water heater, ETC, I do want to hear about explosions nor fires!

Bing carburetors are commonly known to leak in several ways. The most common is fuel dumping on your boot from a grossly overflowing carburetor, typically from a side vent. Sometimes there is just a slow weeping or a slow leak from the very small hole in the bottom of the float bowl.

IF the leak is ONLY a tiny bit of weeping or leak from only that small hole in the bottom of the carburetor:
Remove the bowl, clean the outside bowl area with fine picks, strong solvent, etc.  With the carburetor bowl top surface upside-down onto a flat hard surface such as a thick metal plate, and using a tapered tool of some sort, give the folded-over pipe a modest whack with the tool & a hammer,  This will re-seat & re-stake the tiny pipe. Only in quite rare instances have I had to seal the pipe interface.

There have been rare instances where that tiny pipe has split from the freezing of water in the bowl. If so, the pipe must then be replaced….unless you have a bulging wallet ….then you can purchase a new bowl.   Remember that there are left side, and right side bowls.

There have been instances of splits from the other small pipe. This is the one coming downwards from the carburetor main body, that dips into the bowl corner “well”.  A split causes problems with the choke (enrichener) operation.  That pipe can usually be fixed by soldering a larger pipe over it, but be very careful in your work, and do notice if the downwards pipe has any side holes, if so, those must be maintained in operation.

The Bing Dance, gushing fuel, Part 1:

1. Motorcycle is outdoors, or, otherwise away from flames, etc. Perhaps you are on a trip. Don’t do this in your garage unless it is quite safe from water heaters that might ignite fumes, etc.  If in your garage when the fuel begins to leak, be sure the petcocks are OFF (lever horizontal), and move the motorcycle outdoors, and VENTILATE the garage!

2. Remove the leaking float bowl by levering backwards the small loop in the stiff wire that holds the float bowl to the carburetor main body.

3. Turn on appropriate petcock.

4. Moderately gently jiggle the carb floats up & down with your fingertip to start & stop fuel flow; this usually flushes any filth out of the needle & seat.

5. Petcock OFF.

6. Reinstall float bowl. Install carefully; be sure the gasket is fully in the upper body groove. The gasket must be intact, all-around.


The Bing Dance, gushing fuel, Part 2:

If Part 1 does not wash out the particle of filth that may be in the needle/seat area, or you have float or float needle wear; then you have to dig deeper. It is best not to do this on a trip, due to the quite small parts that may fall out of the carburetor.  Do your work on a flat surface, perhaps covered with a large piece of old white sheet, so any dropping parts are easily seen.   Always keep “FIRE!” in mind.

1. Bike on center-stand.

2. Petcocks OFF; cross-wise for the fuel petcock lever, horizontal, that is. Does your Petcock says AUF? ….you do know what AUF means? You think the German’s have mizzpelt OFF? You think it means OFF?  …..>>REALLY?

3. Remove float bowl & inspect contents. See any water droplets? Know what to do if any water? Yes…you dump contents into fuel tank, but sans water droplets. If you are not Totally Politically Correct (and I am not), dump float bowl liquid contents on the ground or on dandelion weeds. Make sure the float bowl gasket is in good condition & is still fully in the upper body groove for it as you replace float bowl and lock it with the bale wire. It is OK to hold the fuel bowl to the carburetor body, gasket still in the groove, if you do not wish to lock the bowl with the bale wire at this time.

4. With the bowl fully up to the carburetor, turn on petcock, as required, & wait 15 or 20 seconds to be sure float-bowl(s) are fully filled.

5. Turn off the petcock(s).

6. Rather quickly remove the floatbowl, straight downwards & do not spill float-bowl contents. Removing quickly keeps the majority of the fuel left in the fuel hoses from filling the floatbowl fuel level much higher, during bowl removal.

7. Check float bowl on level workbench surface. Yes, it will rest on that round bottom area of the float-bowl. Approximately 2/3 to 3/4 of bowl should have fuel in it. If there is more than that, then your float or its adjustment, and/or needle, is no good.

I do recommend you remove the one-piece float and test it:

With the bowl off, remove the float bowl pin.  The pin is knurled only at one end & is to be removed only outwards from that knurled end. Be cautious & careful, you do not want to bust either of the two pin posts (bosses). Use a tiny drift or make such a tool from a nail….you want a flat end & tiny diameter to fit the floatpin at its non-knurled end. Tap Tap Tap, Tap; gently. If you break the pin boss, prepare to empty your wallet or part of your bank account.

After the float-bowl hinge pin is removed the float will remove (drop out) from the carburetor with the float needle & the float needle’s teeeeeesny wire springy paper clippy thingy. No teensy clip?….very early carburetors did not have them. They are not a critical item. Carburetors that use that clip will be seen to have a quite tiny hole in a spring loaded plunger located at the lower end of the float needle.

Remove the float needle (and clip if you have it) from the float. You probably lost that, or whatever in the GRASS or GRAVEL  you #@(***!!)=+@!! have the bike on. WHY are you doing this in the grass? Why not on a piece of old white bed sheet?

8. Drain sufficient fuel into a glass jar. Put the float into the jar. About 1/3 of the float should be floating above the fuel surface. You need enough fuel in the glass jar so the float does not touch the bottom of the glass. I recommend not using Spouse’s favorite measuring container. If 1/3 of the float is not above the fuel level, the float is bad and should be replaced with a brand-new one.

If you are a terrible cheapskate you could try putting a few small holes in the float, towards the rear (away from the hinge)…. or sanding the float, …or otherwise reducing the float weight to exactly 10 grams…but best away from the hinge so the effect is increased.  OK, so I am sort-of-kidding here.

Let’s assume you are going to properly replace the float and the float needle.

You have a decision to make:
(1) Stock type float?
(2) Bing sells a conversion, the Dual-Independent Float kits, $$$ with the special bowls required. NOT a BMW item. So, below is a couple of short paragraphs about the Bing Independent floats kits:

BMW undoubtedly could have installed these, when they became available, if they thought they were an improvement. I doubt it would have cost BMW any additional money. BMW was likely smart enough to know that adjusting floats 2 or 3 times over a period of months until the adjustment settles down was not great on customer & shop personnel relationships. Much more importantly, BMW likely also knew that these new bowls came without any sort of tiny brass tube sticking upwards, that acts as a relief-vent-of-sorts. Without that vertical tube, a slightly leaky float needle/seat could end up filling the bowl, and maybe dump liquid fuel into the engine’s left cylinder, particularly if the side-stand was being used. Common liquids do not compress. If the left cylinder contains a few tablespoons of liquid fuel….& you try to start the bike, the right cylinder might try to start and run the engine. The left piston will move outwards with great force, striking the liquid fuel, which does NOT compress. This can lead to more than just a bent connecting rod. The piston could break-up and the engine start and toss all sorts of small broken pieces from the piston, etc., into anyplace it can …including the oiling system. The rod could break. A valve could break. Even if the right cylinder did not fire up, the starter motor force might cause left cylinder damage.

We know you are a nice person, and are kind to animals  …and to your bike.   Your motorcycle will appreciate you turning your petcock(s) off when you park the bike ….Bing independent floats kits ……or not!

9. If you have the normal white color single-piece float (it is all one molded item including the metal part) which is the stock float, I suggest you replace it with the same type …unless you really want the Bing dual floats kits.

Once properly set up with that dual-independents floats conversion, & also remembering to always turn the petcock(s)  off  when parking,  and never leaving the petcocks on if using the sidestand, ….. you will likely never have to replace floats again. If you intend to get these pricey conversion kits, read the article on the Snowbum website first. You are too lazy to go look for that article?  Here is a link:  https://bmwmotorcycletech.info/bingindependent.htm

HINT!    BMW dealerships often sell stock parts for your carburetors cheaper (!!) than Bing Agency does. BMW dealerships may not stock the Bing conversion kits …but, heck, ask anyway, they might have them …same for your Independent Servicer.

I am not recommending, nor not recommending the Bing independent float conversion kits. I am simply informing you.

10. ALWAYS replace the float needle at the same time you replace floats. I suggest that you replace the stock type float & float needle every 30,000 miles if you are using modern rotgut gasoline’s. For all Bing CV carburetors, I recommend you replace the diaphragm and center slide needle every 60,000 miles. Clean the carburetor properly & replace all the O-rings except the one in the throttle shaft (unless leaking or you just want to) also every 60,000. There are verbose articles on the Snowbum website about doing those things.

11. It is very easy to loose the teensy-tiny paper-clip type of springy-thingy that clips into the float needle at a hole in the bottom of the float needle…and wraps on the tang of the floats bridge. Those are used only on the float needles that have a plunger with a hole sideways through it. The clip is typically lost when you are replacing the float needle.  Do not loose it.  I suggest ordering half a dozen & keep them on hand. Some put an old white bed sheet under the carburetor, to better find the parts that are going to, otherwise, go into hiding. Do not work on carburetors in the dirt; or on a grassy lawn.

12. For the stock one-piece floats: After you re-assemble the carburetor (without float bowl), adjust the tang on the float assembly (do not forget the float needle & its tiny spring, if used on your carburetor). The need for any tang adjustment is done with petcock on, tang not twisted during adjustment. It must remain flat and horizontal  ….so that as you lift the float very gently & slowly ….the fuel cuts off as the float just passes the point where the float top is exactly parallel with the bottom metal of the carburetor where the bowl gasket fits. Don’t lift the float hardly much past that point. You should be doing all this with a fingertip! Now that you are wet with gasoline (why didn’t you wear plastic or rubber gloves?), you slowly lower the float. The fuel should just barely start to flow with the float top just exactly parallel or a teeny amount lower (not higher). Not that way? Adjust the tang, and re-try.

13. If your floats are the dual-independent type that Bing sells in their kit, they are adjusted differently, so have some coffee, relax, borrow a donut (or three) from the cop next door, & then see my article on my website regarding those floats:

14A. Sometimes there is a wee tiny bit of weeping, just stains usually, at the dome top insert (if you have them, the flat top carburetor model does not). Clean 360° around where the dome plug is staked into the top of the carb, do this with sharp dental picks, and/or very teensy-tiny pieces of fine sandpaper, etc. Clean with a fast drying solvent like acetone. Apply, using a toothpick, a very tiny trace of two-part epoxy, all around that dome centerpiece interface corner. I usually test these dome tops when the carburetor is apart …with the top upside down, …I put gasoline or other solvent into it, to see if the insert is leaking. Some folks like to put a very small BMW roundel on the top insert, using epoxy; if you do, please seal the top plug first. The roundel article has a listing of the appropriate roundels. https://bmwmotorcycletech.info/roundel.htm

14B. If the weeping gas stains are at the junction of the whole top where it meets the body, the fix is different. Besides the unsightly stains, there have been some carburetor functional problems; rare though. Oak sent me (in 1984!!) a bulletin he made up describing this weeping gas stains situation as not necessarily being caused by the lack of the diaphragm acting as a good-enough for its function seal (as some think), but rather that the compression of that diaphragm was insufficient for a complete sealing against the faintest weeping. He recommended removing the carburetor & flat sanding the carburetor main body itself with 220 grit “Wet or Dry” 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; it does stop the staining, and it is possible the carburetors work a bit better too.

Few of you probably have the gauges to measure this groove depth, although it can be done with pieces of known diameter wire and carefully doing a parallel-flat measurement to the wire, so here is what to do if you have no method of proper measurement of the groove depth:

Put the carburetor upside down onto a piece of ~220 grit “wet-or-dry” type of paper, grit size up, on a flat glass or other surface plate. Wet the sanding paper with water. Do ten equally-pressured figure eights, with not much pressure. Rotate the piece during this work (lift, rotate, repeat sanding).  Keep the carburetor flat to the flat surface of the surface plate and the pressure should be kept as even and directly downwards as you can. Once the fresh sanded surfaces are quite evenly seen to be fresh metal all the way around, and a bit more …that is likely enough. Do not overdo this. Clean and reassemble. If you want to measure your work, and know how, reduce the groove depth by 0.007″.  Ten equally-pressured figure-eights requires more sanding than you may think.

15. On a rare occasion, a bowl has cracked, & then typically weeps from a corner via a very slight vertical crack. Replace the bowl. This happened more often on the reddish-brown plastic bowls that Bing used to supply (now metal) with their independent floats kits.

16. Somewhat rare is a leak where the fuel hose fits over the metal pipe at the carburetor. The pipe itself might be leaking where it enters the carburetor. Do not  pull strongly, whether straight or sideways, if removing the hose….cut it off instead.  It is the pulling/bending of the hose that pressures the metal pipe and causes the rare leak.

Don’t try to remove the pipe! First, mind what I just said: remove the hose by cutting it off, not pulling it off (unless very easy to do so, which is seldom). Clean the pipe fitment area with a strong solvent & let it dry. Apply a wicking (thin, watery) grade of Loctite to the junction of pipe & carburetor body. Then put something into/onto that pipe’s end (the easiest is a short machine bolt that fits into the pipe & the head of the bolt fits flat on the pipe top); give the bolt head a modest whack with a smallish hammer. I usually use a small brass or dead-blow hammer. I have a mandrel I made for this job on my lathe, it fits over and into the pipe, but you don’t need one, just use a bolt as described. Next, apply the wicking Loctite again. I let the carburetor sit, that pipe undisturbed, for a couple of days, before cleaning off any residual Loctite.  Waiting allows the Loctite that flowed into the pipe-body junction to set-up and cure.  Repeating myself:  It is quite possible that the original leaking problem was caused by excessive pulling on the hose.

17. Regarding GS (and other later model Airheads) fuel overflowing (slight to more….. perhaps from the bowl).
ALSO: Strange carburetion problems; can include stumbling and funny throttle feel.

The problem has been cause for some strange hard-to-trace-down-problems, because the cause is fuel foaming inside the float bowl. Vibration …at high road speeds usually …can even cause the float bowl to overflow.

BMW issued a Bulletin. The problem, per BMW, is due to the wrong type of rubber hose material, located between the carburetor & the cylinder head. The proper hose is 13-72-1-254-654. The supposedly slightly softer -360 was used by BMW to address foaming in the float bowl. Use the -654, check the fuel level, & adjust the fuel level to be slightly on the high side of specifications. Brand new hoses of both numbers look and feel identical to each other. The diameter is very slightly different, & the rubber construction is very slightly different. They also have those different part numbers on them. I do not use -360 fuel hoses on any Airhead now. The next paragraph describes the problems in a different way, and in more detail, because this paragraph is surely confusing.

In the mid-eighties, BMW made a change to the hose that couples the carburetors to the cylinder head intake stub. BMW softened the rubber compound of the hose. Only 32 mm carburetor bikes went to the USA. THEY had 13-72-1-338-360 hoses. I suggest replacing them with the older style of hose, which was 13-72-1-254-654. You can also try raising the float bowl fuel level by 2 or 3 mm, which applies to both sizes of carburetors. For the mid-eighties and later, 40 mm carbureted bikes were not shipped to the U.S. The Euro 40 mm carburetted bikes had 13-72-1-338-362 hoses and I suggest you change them to 13-72-1-264-392. The true story of this hose change is not all that clear, not even when reading BMW’s bulletin on the subject. Supposedly the problem was first found on the R100GS/PD. I guess that the problem was then found on the R80GS. In any event, two things happened. First, vibration, road shocks, whatever, could cause the float bowl to overflow. BMW also found that there was foaming & frothing of the fuel in the bowl. So, BMW changed to a softer compound in the hose.  It is not easy to test both types of hose with your hand and find out which is which (you mostly have to look at the printed number on the hose!). BMW’s fix did not work well. The new hoses sagged, & over time that sagging got worse. Hoses leaked vacuum. I have seen them look good, but sagged, and no amount of band clamp tightening fixed that. My own 1995 R100RT USA model, had the problem. Do change the hoses as described. Then check the fuel level, ….and run the fuel level slightly on the high side of specifications.    Still Konfuzed?

18. FLOAT NEEDLE SEATS: It is relatively rare to need to replace a float needle seat, and when you need to, it is usually because the seat has deteriorated, possibly from moisture in the carburetor, or? ….and you may find that even a brand-new float needle does not stop overflows even with new hoses that are not shedding particles, and even if adding a pleated paper fuel filter, jiggling the float while fuel is flowing, etc. You may hear that float needle seats are not replaceable or that only Bing can do it. Not so!  Some folks have drilled them & used an EZ-Out to remove the old one. That is not a method I recommend! These seats are rather strongly pressed into place. Heating the carburetor might help; but, even then the heat may not release them; the expansion rate of the materials is not greatly dissimilar. Before you replace a seat, you can try refinishing the seat with a pointy wooden tool to which you apply a bit of FINE-grade valve grinding compound. I do it rather quickly with a pointy wooden dowel and my electric drill using fine grit valve grinding compound.

Here is a seat replacement method that will work, but you can improvise your own:

a. Tap the seat with a 7 mm x 1 mm tap. You could use SAE (American threads) taps too, 5/16″ x 24 perhaps.

b. Use a screw of 7 x 1 mm thread, or 5/16 x 24 American threads if you used that type…maybe 50 mm (2″) or so long.

c. For the metric size 7 mm, you will need some sort of bushing, perhaps about 8+ mm in INSIDE diameter, & about 14 mm or so outside diameter. This bushing should be around 25 mm long. Nothing critical here except that the OD is important so the bushing fits the needle seat surrounding carburetor area, & does not press on the needle seat itself. You can now use that screw and the bushing (and maybe a washer) to draw out the old needle seat. Pin-point heating may help…..as I think the carburetor body material expands slightly faster than the needle seat material. You can also use a common nut for a bushing!

d. Again use heat on the carburetor body, this time when installing the new seat ….which can be carefully tapped into place with a flat tool.

One of these days I am going to, again, hear about someone not turning the petcocks off on an Airhead left in their garage…..in which a natural gas or propane water heater is also located. Could even be something with electrical arcing.   BOOOOOOM!


08/18/2017:   Copied from snowbum website to airheads.org website, and edit for clarity and presentation.
02/19/2021:   Minor emphasis and some changed wordings.

© Copyright 2021, R. Fleischer

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