Why Is My Gas Tank Leaking From The Top!?!?!?

[Waynecarpenter]

I have an original gas tank on my 1966 cb77. It is great condition so I know there is no rust holes. I cannot fill up my gas tank above half way or when I ride itll slush around and come out of the top. My first thought was to change the gas cap gasket. Nope that didn't work. The gas cap itself looks new but I cant be for sure. Here are some pics of what im working with.

[Phil-UK]

Seems they all leak when full but the lip on your tank in the photo looks like it is higher than the surrounding upper surface of the tank. If that is the case then the gasket isn't making contact with that surface. It almost looks domed.
On my CB72 the lip ( i.e. the innermost part that the "ears" go under ) is slightly lower than the top of the tank. Still leaks if full to the brim but OK once the fuel level is @1" below.
Is there another bike or tank you can get a look at to compare ?

Phil

[Goodysnap]

I agree with Phil. Looks like the flange is bent up where the lock tangs grab thus not sealing tight.

Straighten the flange and clean up the gasket surfaces on the tank and cap with a fine scotch brite pad.