Bing Leaking Fuel

[henrysamson]

On my 912ULS there is fuel leaking out the vent line on one of the carbs. It is slow and I am not sure what may be causing it.

Any advice appreciated.

Up to 20 hours of phase one!

Thanks,

Hank

[Dave S]

Hi Hank,

There may be any one of several causes. I'll just throw out some ideas, not saying any them is the actual cause.

1) Fuel bowl overflow can be caused by some problem where the float needle/seat isn't closing properly due to dirt or mechanical binding of some sort - removing the float bowl and investigating what is going on inside the bowl would be a good first item to check.

2) Don't know if you have an earlier Kitfox model with manifolds switched side to side - sometimes that configuration can permit a greater than normal vibration to affect the fuel flow into the bowl; or, a carb socket may be not quite doing its job allowing the carb to bobble around a bit (if you don't have the airbox).

3) How is the vent line positioned? If you don't have the airbox, and the vent line is vented in the engine compartment (that is an assumption I am making - don't know what you actually have), its open end should be in a balance pressure area so there is no vacuum (or pressure) applied to the open end of the vent line

4) Fuel pressure - if the fuel pressure is a bit too high due to an out of spec mechanical pump or boost pump, the line pressure can potentially overpower the float needle and cause a high fuel level or bowl overflow.

Sincerely,

Dave S.
KF7 Trigear
912ULS
Warp Drive
St Paul, MN

[P Morel]

If it's a constant leak, then the float in the bowl may not be working properly or the brass leaf tab may need a little adjustment. If you decide to make any adjustment in the leaf tab, consider the angle of the of the carbs. What I mean to say is there is an obvious difference in the engine and carburetor angle while on the ground of a tail wheel and a nose wheel kitfox.

If the fuel is venting on occasion, then that may be due to the carb vibration. The vibration sometimes won't allow the float needle to seat and fuel will vent. The Bing carbs are further away from the centerline due to the oil reservoir tank being positioned closer to the centerline. My problem in the past has been after landing (tail wheel) and lower RPM the smell of raw fuel. (carb venting)

Some members have made small fuel reservoirs to capture the venting fuel from spilling into the engine compartment as safety is the first priority.

[henrysamson]

If the fuel is venting on occasion, then that may be due to the carb vibration. The vibration sometimes won't allow the float needle to seat and fuel will vent. The Bing carbs are further away from the centerline due to the oil reservoir tank being positioned closer to the centerline. My problem in the past has been after landing (tail wheel) and lower RPM the smell of raw fuel. (carb venting) .

I Think this may be the case as I get a good wiff of fuel right after landing. Further investigation indicated that both have the leak. I get no odor in flight but as soon as the tailwheel comes down . . .

Thanks for the ideas!