Bing Carburetors that pee gasoline onto your boot; or,
leak onto the floor of your garage.....
and some that just WEEP a bit...
How to do the Bing Dance!
© Copyright 2012, R. Fleischer
For float testing in depth: http://bmwmotorcycletech.info/bingcv.htm
For actual fuel level measurements & information on replacing float needle SEATS:
Bing carbs have been 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, but sometimes also from the teensy hole in the bottom of the float bowl. IF the leak
is ONLY a tiny bit of weeping or very tiny leak from ONLY that teensy hole in the bottom
of the carburetor....then remove the bowl, clean the area with fine picks, solvent, etc. Use
a taper tool of some sort, & give the folded-over pipe a modest whack with the tool & small
hammer, with the carburetor bowl top surface DOWN onto a flat hard surface. This will
re-seat/re-stack the tiny pipe. Only in the rarest instances have I had to seal the pipe
interface. NOTE!....in rare instances the pipe has SPLIT from frozen water in the bowl!...the pipe must then be replaced....unless you feel a bulging wallet, then you can purchase a whole new bowl.
It is very important to turn off the petcock(s) when you park your bike. This is still so even if you have a later model Airhead that still has the fuel-shutoff solenoid valve located on the inside of the cover over the starter motor. It is SUPER important if you park your bike in your garage where there is a source of gasoline fumes ignition...like a water heater, ETC. We do NOT need to hear about BOOOOOM! nor FIRES!
The Bing Dance, 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.
2. Remove the leaking float bowl by levering backwards the small loop in the float bowl holding stiff wire.
3. Turn on petcock(s).
4. Gently jiggle the floats up & down with your fingertip to start & stop fuel flow; this USUALLY flushes any filth out of the needle & seat.
5. Petcock(s) OFF.
6. Reinstall float bowl...gasket is fully in the upper body groove; install carefully.
The Bing Dance, 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 needle wear; THEN you have to dig deeper. It is best not to do this on a trip, due to small, even teensy parts that may fall out of the carburetor, etc.
1. Bike on center-stand.
2. Petcocks OFF; cross-wise for the 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 the contents. See any water droplets? Know what to do if any water? Yes...you dump contents into fuel tank, sans water droplets. If you are not totally Politically Correct, 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. 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.
4. With the bowl up to the carburetor, turn on petcock, one or both, & wait 15 or 20 seconds to be sure float-bowl(s) are fully filled.
5. Turn OFF petcock(s).
6. QUICKLY remove the floatbowl, straight downwards; do not spill float-bowl contents. Removing quickly keeps the fuel left in the lines from hardly at all filling the floatbowl fuel level any higher, during removal.
7. Check float bowl on level workbench surface. Yes, it will rest on that round bottom area of the floatbowl. Approximately 2/3 to 3/4 of bowl should have fuel in it. If there is more than that your float and/or needle is no good. I do recommend your remove the float and test it, and here are the details:
With the bowl off, remove the floatbowl pin, it is knurled & is to be removed only outwards from that knurled end. Be cautious & careful, you do NOT want to bust either of the 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, Cry Me A River.....and prepare to empty your wallet or part of your bank account.
After the float-bowl hinge pin is removed the float will remove from the carburetor with the float needle & the float needle's teeeeeesny wire springy paper clippy thingy clip. NO CLIP?....very early carby's didn't have them. They are not a critical item. Carburetors that use that clip will be seen to have a TINY hole in a PLUNGER at the FLOAT NEEDLE lower end. Do remove the float needle (and clip if you have it) from the float. You probably lost these in the GRASS you #@(***!!)=+@!! have the bike on. WHY are you doing this in the grass? Why not on an old white bed sheet?
8. Drain some 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 highly recommend not using Spouse's favorite measuring container. If at least 1/3 of the float is not above the fuel level, the float is bad.
If you are a terrible cheapskate you could try putting a few small holes in the float and reducing the float to 10 grams. No, I've never tried it. So, let's assume you are going to, properly, replace the float (and the float needle). You have a decision to make: Stock type float? Bing sells a conversion, the Dual-Independent Float kit, $$$$ with the special bowl. NOT a BMW item. So, here's a couple of short paragraphs about the Bing Independent floats kits:
BMW undoubtedly could have installed these if they thought it was 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 the 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. Liquid does not compress. If the left cylinder contains a few tablespoons of liquid fuel....& you try to start the bike, the RIGHT cylinder MIGHT fire, and the left piston will rise, at speed, with great force, & strike 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 into anyplace it can...including the oiling system; heck, the rod could break. Even if the right cylinder did not fire, the starter motor force might cause left cylinder damage.
We KNOW you are the NICE type, and even remember to be NICE to YOUR BIKE, which 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 whitish-colored single-piece float (it is all one molded 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 conversion, & remembering to ALWAYS turn the petcock(s) OFF when parking, AND NEVER EVER LEAVING THE PETCOCKS ON IF USING THE SIDESTAND, ..... you will likely never have to replace floats again. If you intend to get these conversion kits, read the article on this website FIRST. You are too lazy to go look for that article? OK, I WILL BE NICE: http://bmwmotorcycletech.info/bingindependent.htm
HINT!! BMW dealerships sell stock parts for your carburetors, often cheaper (!!) than Bing Agency does. BMW dealerships usually do not stock the Bing kits...but, heck, ask anyway, they might have them...same for your Independent Servicer.
10. ALWAYS replace the float NEEDLE at the same time you replace floats. I strongly suggest that you replace the STOCK type float & float needle every 30,000 miles if you are using modern rotgut gasolines. For all the Bing CV carburetors, I recommend you replace the diaphragm every 60,000 miles (aluminum central jet needles then too, steel ones maybe), & clean the carburetor properly & replace all the O-rings except the one in the throttle shaft (unless leaking or you want to) also every 60,000. Naturally, there are verbose articles on this 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 on the float needles that have a plunger with a hole sideways through it. It is typically lost when you are removing it, because 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. If you do your work in the dirt; or on a grassy lawn, etc.......well, I won't say what I think.
12. After you re-assemble the carburetor (without float bowl), ADJUST the tang on the float assembly (do NOT forget the float needle & its TEEEENSY 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 (you get to use #1 eyeball) 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. Don't lift the float past that point...and you should be doing all this with a fingertip! Now that you are gasoline-y (why didn't you wear 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 that way? Adjust the tang, and re-try.
13. If your floats are the dual-independent type that Bing sells, 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 on these float setups:
14A. Sometimes there is a wee tiny bit of weeping, stains actually, at the dome top INSERT. Not all Bing CV carburetors have an insert, some tops are also flat. Clean 360° around where the dome plug is staked into the top of the carb, do it with dental picks, teensy-tiny pieces of fine sandpaper, etc. Clean with a fast drying solvent like acetone. Apply, using a toothpick, a very tiny trace of epoxy, all around that interface corner. I always 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. The roundel article has a listing of the appropriate roundels. http://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; even more rare though. However, 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 seal (as some think), but rather that the compression of that diaphragm was insufficient for a COMPLETE sealing. He recommended removing the carburetor & flat sanding the carburetor main body itself, at the top (obviously the top dome is removed), 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. Frankly, few of you have the gauges to measure this, 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 sandpaper, grit size up, on a flat glass or other surface plate. Use wet/dry paper wetted with water. Try just TEN equally-pressured figure eights, medium light pressure. Rotate the piece during this work. KEEP THE CARBURETOR FLAT TO THE FLAT SURFACE!! Once the fresh sanded surfaces are quite evenly 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".
15. On a rare occasion, a bowl has cracked, & weeps from, typically, a corner vertical crack. Replace the bowl. This happened more often on the reddish-brown PLASTIC bowls that Bing used to supply (now metal) with the 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. Don't try to remove the pipe! First, remove the hose. Then clean the area with a strong solvent, let it dry. Apply a wicking (thin) grade of Loctite to the junction of pipe & carburetor body. 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 SMALL 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 for a couple of days before cleaning off any residual Loctite and that also allows the Loctite that flowed into the pipe-body junction to set-up and cure. It is quite possible that pulling on the hose, pulling sideways, etc., is the cause of the leaks, so avoid doing that.
17. GS (and other later model Airheads) fuel overflowing (slight to some, perhaps, from the bowl)...and 'strange' carburetion problems; can include strange stumbling, funny throttle feel.
This has been the cause for some very strange hard-to-trace-down problems, because its cause is fuel foaming in the float bowl. Vibration....at high speeds usually...can cause the float bowl to overflow.
BMW issued a Bulletin. The problem 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 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 nearly identical to each other...well, almost. The diameter is very slightly different, & the rubber construction is very slightly different. They also have different part numbers ON THEM. I do not use -360 fuel hoses on any Airhead now.
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 slightly stiffer 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 carbed 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. NOTE that 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. The new hoses also sagged, over time that got worse. Hoses LEAKED vacuum I have seen them look good, but sagged, and NO amount of band clamp tightening fixed that. In fact, my own 1995 R100RT USA model, had the problem. DO CHANGE the hoses as described. THEN, also check the fuel level, and run the fuel level slightly on the high side of specifications.
18. FLOAT NEEDLE SEATS: Relatively rare. Sometimes there is a need to replace a float needle SEAT, usually because the seat has deteriorated, possibly from moisture in the carburetor, or? and you have found that even a brand-new float needle does not stop overflows even with new hoses and 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 valve grinding compound. I do it rather quickly with a pointy wooden dowel and my electric drill using FINE 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 14mm 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, not 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 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.
09/22/2012: Add QR code, change Google code; minor other 'stuff'
10/27/2012: Add a bit to item #16, about not pulling on the hose.
11/04/2012: Expand #18
05/07/2015: Fix hyperlinks coding. Fairly extensive editing; and clean things up.
01/29/2016: Update meta-codes. Narrow article. Increase font size, etc.
05/22/2016: Final updating of code and scripts, layout, cleanup, etc.
08/02/2016: Renumber article, was 12B. Fix metacode, had two head tags, miscl.
© Copyright 2012, R. Fleischer
Return to Technical Articles List Page
Return to HomePage
Last check/edit: Tuesday, August 02, 2016