Fuel transfer imbalance in Citabria

[drbrown]

I have a 1999 7GCAA. I've noticed that the fuel transfer is generally very uneven. I can understand it happening while maneuvering, but during XC flights, one side or the other still goes down much more than the other causing an imbalance even though I'm aggressive about maintaining coordinated and wings level flight. Sitting on the ground for some time after flight, the tanks slowly but consistently balance themselves out. The fuel gauges appear to be accurate. The pilot's operating manual says that improperly secured fuel caps will result in fuel leakage and unequal fuel feed. I can't find any evidence of leaking fuel, and the fuel tank caps have been checked and appear to give a good seal. In fact, because of this issue, I bought brand new ones, but still have the problem. On a recent long XC flight, I started with full tanks. After an hour, the left tank was down below 3/4 and the gauge on right was just barely bouncing off full. As the flight progressed, the left side continued down and while the right did transfer, it stayed near full. By the time I landed, I had well under 1/4 tank on the left, about 3/4 on the right (and a real tight butt). On the return flight, it wasn't as pronounced, but I still had the imbalance. So I got a coupla questions:
-The big one is, is this normal for the Citabria?
-If not, what could be the cause? A pinched fuel line? Debris or a bug nest in the vent probe under the left wing? Or a blocked line from the probe?
-How can I trouble shoot to find and correct the problem?
-If I just blow into the vent tube on the left wing, will it damage anything? If I blow into the tube, should there be resistance, or should I be able to blow bubbles in the tank(s), (assuming the caps are off) to verify there is no blockage?
-The really big question is, if I let the imbalance continue to where one side goes dry with lots of fuel in the other tank, will the engine quit due to fuel starvation? Or will the high side naturally start pulling more and supply enough fuel to run the engine, even though it's sucking air on the dry side?

Please send opinions or responses to dbrown@ewa.com.

Thanks for your help., Dave Brown

 

[osxuser]

The engine SHOULD never quit, but that isn't really a normal condition in my experience either I'm guessing a venting issue, but you seem to indicate that it isn't consistently one side or the other, which makes me wonder how that could be.

 

[Ron86654]

Dave,

Go to the "search" box in the upper right corner and enter "uneven fuel". You will find about 44 posts that cover this with several remedies.

Hope this helps.

Ron

 

[sgabrick]

I had the same problem in my 1978 GCAA.

Turned out to be an obstruction in the cross venting part of the fuel system.

Removed the cross vent tube that runs thru the cockpit at the top of the windscreen and discovered a partial blockage in the tube coming from the left tank. Cleaned it out and all is well.