Hello Stefan, I have had the same issue with several cars. Gaskets never seem to do any good no matter how thick they are. The reason is the heat is transfered directly through the mounting studs to the carb. Until you isolate those it will continue to percolate. The best solution I have found is to mount a 3-4 PSI pump near the tank, and run it when the ignition is on. I have an R2, a 62 fuel injected Corvette, a 32 Chevy and a 96 Sea Ray boat I'm doing this with now with no issues.
Best of luck, John C.
