Fuel leak & right tank won't feed

[Champ58P]

Hello!
I have a 1963 Champion 7GCB (150hp, flaps, round tail). Has just one fuel guage for the right tank only.
Just noticed fuel leaking from the fuel float indicator window in the top right wingroot during flight, and correspondingly, the right tank didn't seem to be feeding during flight. Left tank fed normally, but right tank decreased to 3/4 and stopped (and leak stopped except during sloshing). As I watched it leak around the fuel indicator window, I noticed air blowing the fuel quickly away, as though the airstream was taking it out the rear of the wing.

Fuel caps were on tight. This plane has a single vent tube on top of the left wing root, with a cross vent tube going to the right tank across the top of the cockpit by the top glass. Just prior to noticing this problem, I noted an increasing left tank usage relative to the right tank during the two previous refuelings. Prior to that, both tanks would always take the same amound of fuel. Until I sort this out, I am assuming the right tank is now unusable.

Anyone ever faced this problem before? Could there be a vacuum caused by the leak, preventing the right tank from feeding? Or something else? What is involved with repairing that float indicator window leak? Anything else I should investigate?

At this point, I feel like I have half an airplane...any advice would be most appreciated.
Thanks much.
JJ

 

[Champ58P]

Think I have the 7GCB's fuel tank/leak/no-flow problem fixed:
After talking with the great guys at American Champion, I ordered a new gasket for the fuel float gauge, as well as two new fuel filler caps. They indicated that the leak around the fuel guage could have caused a vacuum which might possibly have resulted in the tank's failure to feed.

A&P replaced the gaskets, which were two small thin circular pieces of rubber (removed the fairings on the wings to access the float gauge area) and found a deteriorated, cracked set of leaking gaskets. Gaskets replaced, and no fuel system blockages detected. Gas now holds fine in a full tank without leaking. Apparently an easy fix, and we'll see how the tank feeds inflight soon, now that the leak-induced vacuum has been eliminated.

This was a restored 1963 Champion 7GCB...with very few total hours in the air (I think less than 400 total since '63...) but a lot of years on the these particular pieces of rubber. I noticed the fuel filler caps also had cracks in the rubber, so I'll prevent similar vacuum-induced fuel flow problems with a new set. The peace of mind is worth the price of these new caps.

With aging Citabrias, I expect this problem may begin to occur with more folks as the years go by...I didnt' find a lot of hits on this type of fuel flow problem on the net, so hopefully my experience will help a few folks later on. I also recommend everyone eyeball the integrity of the rubber gaskets in your fuel filler caps next time you put gas in - if they're cracked badly, a vacuum could develop, resulting in fuel holding in the tanks.

Here's the most important lesson for these early Champions- if you have only one fuel gauge for two tanks, always be very suspicious of the quantities and monitor the balances closely. While this is obvious (of course it is, and we All always do this), this event occurred to me on a long cross country hop, and my nagging feeling of "I shouldn't have that much gas in that right tank at this point" (it was feeding but slower than the normal rate) caused me to make the decision to land a lot sooner than I had planned and helped me avoid a big problem...had I trusted the guage at face value, I might have continued and found myself unhappy with an empty left tank and a slowly or non-feeding right tank.

Regardless of your type of aircraft, consider this post a great reminder for everyone on the importance of fuel management and continuous fuel quantity awareness. Plan contingency fuel stops along your cross country route in case of events like this one.
JJ

 

[Champ58P]

Fuel is feeding equally now from both tanks. after repairing the fuel gauge gasket.

For me, this confirms that the fuel leak, which occurred as a result of a dry-rotted gasket around the wingroot floatgauge, was also causing a vacuum in the right tank. This vacuum was causing fuel in that tank to stay in the tank with suction, preventing it from going down to the engine, resulting in an imbalance. Fuel leaked from the tank into the slipstream down to 3/4 tank (where the fuel gauge gasket was deteriorated), then the hole there caused a vacuum which resulted in a fuel flow problem.

Based on my recent experience, I'd say this is probably a useful bit of Champion/Citabria corporate knowledge, and I hope others will take a good look at those fuel gauge gaskets and gaskets on the inside of the filler caps. If anyone else has a better informed perspective on this problem, I'd be happy to learn more.

JJ