New-to-me bike obtained from a friend. Bing slide carbs with ticklers and no choke cables. Carbs reportedly professionally rebuilt in the past year after bike spent decades in storage. Gas drips from the bottom of the float bowl whenever petcock is on. It does not seem to be coming from the top of the bowl where the gasket is. Float looked a bit old, so I replaced it and checked to see that fuel doesn't flow when it's in the up position. The gasket for the float bowl drain plug was not in stock at local BMW dealer parts dept, so I didn't swap that yet (and known substitutions?).
My right boot stinks of gasoline, I've averaged 35mpg, and I'm itching to take some longer trips, so I need to fix this pronto.
Sounds like you've done all the right checks. My R60/6 has the manual chokes, so not sure if the tickler could be the issue or not. Sounds like you checked that the gas flow stopped by lifting the bowl float manually with the bowl removed. Just be sure when you do this that, at the poing the flow stopped the float is parallel to the bottom edge of the carb body.
G
Those type leaks usually fall into 1 of 4 solutions....
@ New fuel is cleaning the fuel tank of old fuel residue, some of which has washed down to the float valve and is holding it open. This will be a minute speck of trash, about 1/4 the size of a small grain of sand. If you hope to see it you mush work over white kitchen paper towels. Blowing air or carb cleaner through the inlet into the float area usually washes it out. This may occur 2 or 3 more times before the tank is thoroughly clear of trash.
This can also take the form of caked on fuel deposits on the float seat area itself. These need to be scrubbed off with carb cleaner and a wooden dowel, so as not to scratch the seat.
@ Incorrect float level due to the combination of new float and/or new float needle. Typically Bing does not give a dimension, but rather the simple instruction to make the float parallel to the carb base BEFORE any spring in the float needle is depressed. To do this, the carb is held upside down at 45 degrees so that some of the weight is applied to the float needle, but not enough to depress the spring (if one is present).
@ Broken or mal-formed tickler return spring, causing the tickler to continue to depress the float. This is easy enough to measure or visually check and rule out.
@ Damaged float bowl gasket. This is your LEAST likely scenario. However, it is likely that trash could be holding the bowl off the gasket OR that the bowl is installed but not properly seated due to working in positions that do now allow full visual inspection. (I cannot imagine a better excuse for buying a platform lift !! 😛 )
One has to realize that the float bowl gasket is typically far above the average fuel level. So the fuel should never come as high as the gasket. The gasket then only protects against splash. Far more likely that the fuel is coming through the brass over-flow tube pressed into the float bowl. Then down the tube and onto your shoe. Jap carbs have the same device, except they have an external nib onto which a small hose is connected. Owing to the close proximity of the rider's foot, an external tube cannot be used on the BMW. Without the external hose, the fuel seems to materialize from no where making diagnosis harder. Dust the area with talc or flour and turn ON the fuel. It will be easy to find then.
Hope this helps.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Thanks for such a detailed answer. I'll have some garage time tomorrow to work my way though that list. -Chris
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