Hey guys. I have a question about the gas cap on my 65 Mustang. It has a rubber gasket that seals the cap to the filler tube. Should the rubber be thick enough to completely seal the cap, to the point where I hear a hissing noise of pressure releasing when I take the cap off when filling the tank? The rubber gasket that came with the new gas cap seemed kind of wimpy and thin, so I cut a thicker piece out of rubber and installed it. I'm wondering if it will make it hard for the motor to suck the gas to the carb if there is a completely sealed tank.