gas tank

i sold my 1979 kz1000 shaft driven to my friend i was told this style bikes have problems with the gas tank leaking when you fill it. we put a new rubber gasket and still having problem is there anyone who has this problem and fixed it.

Yeah, the sidestand makes the bike lean over a lot and this makes the leaking worse. There is a large round gasket that you have found but you will have to take the gas cap off to find the other gasket inside the cap. Also, if the orings that go around the mount screws are worn, replace them. The cap may not be sitting down tight enough. I have a 79 KZ1000E and had to do these things to keep the cap from leaking.