Bing CV Carburetors that pee gasoline onto your boot; or,
weep or leak onto the floor of your garage.
How to do the Bing CV Dance!
Fuel foaming from vibration, particularly on GS models.
Float needle seat replacement. New float installation.
© Copyright 2017, 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 motorcycle. This is so 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 such valves have been removed, but the same caution applies). It is exceptionally important if you park your bike in a garage where there is a source of gasoline fumes ignition ...such as a water heater, etc. We do NOT need to hear about BOOOOOM! Nor FIRES!
Bing CV carburetors are commonly known to leak....and somewhat rarely, to have problems with an internal tiny pipe used in the enrichener (erroneously call the Choke).
The most common is fuel dumping on your boot from a grossly overflowing carburetor, typically coming 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. The top may leak where it fastens to the body, usually this is a very faint weeping, leaving stains, and no liquid fuel is seen. Rarely there is a leak from the area of the metal pipe the goes into the side of the carburetor; this is where the fuel hose pushes onto. Other leaks are quite rare.
Eventually all stock Bing CV carburetors (and some non-CV types too), will leak. The cause can be more than one thing, but commonly it is float old age; deterioration of the float from being immersed in fuel (modern fuels tend to be poor) for a quite long period of time. It is difficult to, then, say at what mileage floats should be replaced (always with a new float needle), but certainly not over 60,000 miles, and doing it at half that mileage is not at all out of the question.
If the leak is a tiny bit of weeping or small leak from the small hole in the bottom
of the carburetor bowl:
Remove the bowl, clean the outside bowl area with fine picks, solvent, etc. Use a taper tool of some sort, & give the folded-over pipe a modest whack with the tool & via a small hammer, with the carburetor bowl top surface DOWN onto a flat hard surface such as a thick metal plate. This will re-seat & re-stake the tiny pipe. Only in extremely rare instances have I had to seal the pipe interface. There have been rare instances in which the tiny diameter upwards going pipe from the bowl has SPLIT from frozen water in the bowl! If so, the pipe must then be soldered or replaced or a sleeve fitted ....unless you feel a bulging wallet, then you can purchase a whole new bowl.
There have been instances of problems but these do not cause leaks, from another small but slightly larger pipe. This is the one coming downwards from the carburetor main body, that dips into a bowl corner well. It splits from water and freezing. This causes problems with the choke (enrichener) operation. It too can be sleeved, or soldered.
The Bing CV Dance, Part 1:
(The carburetor gushes fuel)
(There is a tendency for this to happen awhile after parking the bike, and leaving the fuel petcock(s) in the ON position).
The cause can often be a well-worn-aged float, because the fuel level has been very slowly rising for a very long time, and your day for gushing is when you, perhaps, put the bike on the sidestand......but mostly the cause is a float needle seat that is not perfectly sealing, and while this can happen from a bad seat, it is not uncommonly simply an old worn needle tip that has a slight groove in it, and should be replaced. MOST OF THE TIME the cause is simply a microscopic bit of filth that has lodged itself in the needle/seat area, and that is very common, and can be filth that got by the screens in the petcock (or, aftermarket one below the petcocks, rarer then, though), or, a particle from a deteriorated fuel hose just above the carburetor. The procedure here in Part 1, is to try to easily remove that bit of filth. If this does not fix things, and gushing fuel returns fairly often, install a new float needle ...and....you need to install an aftermarket fuel filter below the petcock (assuming you do not already have one), clean petcock screens, perhaps clean the fuel tank, and do inspect the fuel hoses condition, carefully. In egregious cases, you must inspect the needle seat. Replacing the needle seat can be done by you, but the procedure is a bit involved. The Bing Dance follows:
1. Motorcycle is outdoors; or, otherwise away from flames, etc. Perhaps you are on a ride or trip. Don't do this in your garage unless it is quite safe from water heaters or other things, including electric, that might ignite fumes, and you have PLENTY of ventilation. The motorcycle should be on its center-stand.
2. Turn the fuel petcocks to the horizontal off position. Remove the float bowl by levering backwards the small loop in the stiff bale wire that holds the float bowl to the carburetor.
3. Turn on appropriate petcock, which will cause fuel to flow rapidly.
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. Do NOT be aggressive in the amount of pressure from your finger.
5. Petcock OFF.
6. Reinstall float bowl carefully. Be sure the gasket is fully in the upper body groove. The gasket MUST be intact, all-around. If not, it must be replaced as soon as you can. The gasket is often torn by ham-fisted owners at the corner well at where the enrichener tiny pipe sticks down from the body and the enrichener will not work adequately on a cold morning if that is so. Use your fingers to push the bale wire fully into place.
The Bing CV Dance, Part 2:
(If Part 1 doesn't remove the 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 in the later portion of these tests/adjustments)
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 your old fuel can that you keep around for such garbage things. Yes, I know you will likely dump the float bowl liquid contents on the ground or on dandelion weeds. Leave the bowl off the carburetor. Where did the water globules come from? Spraying the carburetor from your hose? Water in the fuel tank? ???
4. Check the float adjustment. Turn the petcock ON. Fuel will gush out. LIFT the float with your finger tip, not too vigorously ...until the fuel just shuts off, lower slightly, repeat. Find the point, exactly, where the fuel JUST shuts off. At that point, the TOPS of the floats should be parallel with the bottom of the carburetor casting. If it is not so, you need to adjust the float tang. For a finer check on adjustment, check where the fuel just barely flows. Now, fuel OFF, replace the bowl (mind that gasket!).
5. With the bike on the center-stand, and with the bowl fully up to the carburetor, turn on petcock & wait 20 seconds to be sure float-bowl is filled to whatever level the float and needle allows. Turn OFF petcock.
6. MODERATELY 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 the bowl on level workbench surface. Yes, it will rest squarely on the bottom area of the float-bowl. Approximately 2/3 to 3/4 of bowl should have fuel in it. If there is more than 3/4, then your float and/or needle, is no good. It is time to actually weigh the float if you have a fine gram scale ....otherwise, install a brand-new float AND float needle. If you have the fine wire clip, order a few extras at the same time you order the float and needle.
8. Removing the float and testing it (even if you do not have a gram scale, DO this test):
With the bowl off, remove the float bowl 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 and a grinder;....you want a flat end of 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, so be gentle.
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 SUCH 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 TINY hole in a PLUNGER at the lower end of the FLOAT NEEDLE. Early float needles were all metal; later ones have a rubber tip.
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? WEIGH the float unit if you have a good scale. 10 grams. If over ~12, the float is BAD for sure...but, may be usable for awhile. You need to do the next test, which is fairly definitive.
9. Drain sufficient fuel into a glass jar. Put the float, without its pin, 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.
If you are a terrible cheapskate, or have some other reason, you could try putting a few small holes in the float or sanding the float, and reducing the float weight to 10 grams, or so it floats properly. No, I've never tried either.
10. So, let's assume you are going to, properly, replace the float (and the float needle).
You have a decision to make:
a. Stock type float?
b. Bing sells a conversion, the Dual-Independent Float kits, $$$ with the special bowls required. NOT a BMW item.
Below is a couple of paragraphs about these kits:
BMW undoubtedly could have installed these LONG AGO, if they thought they was an improvement. I doubt it would have cost BMW any, or hardly 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 from the bottom of the bowl, 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. Gasoline liquid does not compress. If the left cylinder contains even just 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 rise with great force, & strike the liquid fuel, which, remember, 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, the starter motor force might cause left cylinder damage.M/p>
We KNOW (??) you are nice to your bike, so you always (?) turn your petcock(s) OFF when you park the bike. No matter if you have stock floats, or Bing independent floats kits, and no matter if the bike is on its center-stand or side-stand! In fact, even if you a late model still having its electrically operated fuel solenoid valve under the starter motor cover, you shut off the petcocks. Correct?
11. If you have the normal stock/standard single-piece float (all one molded item including the metal part), I suggest you replace it with the same type; unless you really want the Bing dual floats kits. Once properly set up with the dual-independents floats conversion, & also 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. Yes, you WILL have to replace the float needles now and then. If you intend to get these conversion kits, read the article on this Snowbum website FIRST. You are too lazy to go look for that article? Here is the link:
HINT!! BMW dealerships sell stock parts for your carburetors, often cheaper!... than Bing Agency does. BMW dealerships usually do NOT normally stock the Bing conversion kits ...but, heck, ask anyway, they might have them ...same for your Independent Servicer.
12. 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 float needle, even if you have the independents kits, at 30,000 miles; and, on all CV carbs, 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. Naturally, there are verbose articles on the Snowbum website about doing those things.
13. 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 it wraps around the TANG of the floats bridge. Those are used only on the float needles that have a plunger with a hole sideways through it. It 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 otherwise disappear. Do NOT work on carburetors in the dirt; or on a grassy lawn.
14. 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 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 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 that way? Adjust the tang, and re-try.
15. If your floats are the dual-independent type that Bing sells in their kit, they are adjusted quite 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: https://bmwmotorcycletech.info/bingindependent.htm
16A. Sometimes there is a wee tiny bit of weeping, stains are what is usually seen, at the dome top CENTER INSERT. Not all Bing CV carburetors have an insert, some tops are flat. Clean 360° around where the dome plug is staked into the top of the carb (restake if noticeably loose), do scratch cleaning too, with dental picks, very teensy-tiny pieces of fine sandpaper, etc. Clean with a fast drying solvent like pure acetone. Apply, using a toothpick, a very tiny trace of two-part epoxy, all around that interface. I usually first 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 or during the roundel epoxying. The roundel article has a listing of roundels. https://bmwmotorcycletech.info/roundel.htm
16B. 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, 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 numerous 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. 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, not much pressure. Rotate the piece during this work (lift, rotate, repeat sanding). KEEP THE CARBURETOR FLAT TO THE FLAT SURFACE AND THE PRESSURE EVEN AND DIRECTLY DOWNWARDS. Once the fresh sanded surfaces have nice clean evenly fresh metal all the way around, ....and a bit more ....that is likely enough. Do not overdo nor underdo this. Clean and reassemble. If you want to measure your work, and know how, reduce the groove depth by Oak's 0.007".
17. 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. I know of nothing that is a permanent sealer for this.
18. 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! Do not yank hard on that hose! First, remove the hose by cutting it off, not pulling it off (unless very easy to do so, which is seldom). You can make a U shaped tool to try to slide the tool between hose and carburetor, but usually the hose is fully-on. IF you CAN get such a tool in there, then lift on the tool a bit, as you pull lightly on the hose. That eliminates the Chinese pull-toy problem with removing the hose. In any case, remove the hose.
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. 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 possible that the original leaking problem was caused by excessive pulling on the hose, or pulling sideways.
19. GS and other later model Airheads fuel overflowing (slight to more; .....perhaps from the bowl).....
(Also covered .... strange carburetion problems; including stumbling and funny throttle feel):
This has been the cause for some strange hard-to-trace-down problems, because the cause is fuel foaming in 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, was 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; that means the fuel shuts off with the float a bit further upwards than parallel. Brand new hoses of both numbers look and feel nearly identical to each other. The diameter is very slightly different, & the rubber construction is very slightly different. They also have different part numbers located right 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.
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. The Euro 40 mm carburetored 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 should look at the printed number on the hose!). BMW's fix did not work well. The new hoses sagged, over time 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, also check the fuel level, and run the fuel level slightly on the high side of specifications.
20. FLOAT NEEDLE SEATS: It is relatively rare to need-to replace a float needle SEAT, and when you must, it is usually because the seat has deteriorated, possibly from moisture in the carburetor, or? ....and you find that even a brand-new float needle does not stop overflows even with new hoses (or, needle fails very soon) and adding a pleated paper fuel filter, jiggling the float while fuel is flowing, etc. do not help. 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, because it may not work well, and you can badly damage the carburetor. The seats are rather strongly pressed into place. Heating the carburetor may help; the expansion rate of the carburetor material is greater than the needle seat. Before you replace a seat, you can try refinishing the seat with a pointy wooden tool to which you apply a bit of fine grit 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. 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 the carburetor body material expands 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 or other method.
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. Actually, with enough gasoline fumes, almost anything will set it off. BOOOOOOM!
Revisions: © Copyright 2017, R. Fleischer
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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.
06/06/2017: Reduce colors and font changes.
06/21/2017: A few clarifications and some colors, underlines, bolds, T-A-L info listing, and metacodes fixed.
12/12/2017: Rework entire article for clarity, less html, fewer font and colors changes, add 10pxl margins.
12/15/2018: Slightly clarify details on removing and replacing a carburetor float needle seat.
© Copyright 2017, R. Fleischer
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Last check/edit: Monday, July 22, 2019