The Cessna 120-140 Association Forum

I have a 1946 140. I have had it for 5 years and until this year have flown it about weekly. The past few months I have not been able to fly it as frequently so it sits in the hangar for longer periods between flights. I have noticed that after not being flown for 3 to 4 weeks the left tank loses fuel. The loss is about 2 gallons over a month. I do not see a change in the right tank. I always fill both tanks before putting it back in the hangar. I do not see any sign of leakage on the wing or floor. I have asked a couple of mechanics what they think and they aren't sure what is going on. I have seen some possible issues when searching online such as a damaged fuel cap gasket, fuel possibly leaking into the carburetor due to a valve issue and then evaporating or flowing into the other tank. I also have read about issues with pin hole leaks in the tank with the fuel evaporating inside the wing. I am hoping to find the most common cause and or insight into this type of fuel loss. Thanks.

dliptrap,

You don't sat whether you have fabric or metalized wings. I can't speak about fabric wings, but having now replaced both fuel tanks in my metalized wings, from the amount of blue "goo" found in my wings, its clear my tanks had been leaking for a long time without obvious external signs. I'm in Arizona and the fuel evaporates quickly. The evaporation rate may be different where you are. Pull the wing root fairing and see if there's staining (you won't be able to see the tank).

Stromberg carb needle seat? Shut fuel off at selector to check over time.

Thank you

My wings are fabric. Thank you for your comment.

Do you have a "both" position on your fuel selector? What position do you leave the fuel selector in when you park it?