Hi steve ,

you are right but the tank is not always full and thus most of the time there would be some air on top of the fuel and this will make a air-fuel mix .
anyway i have to think it would be enough to make a explotion !

In other hand you're completely right .i haven't seen any diodes or other protections on any of the GM productions (from 1970 to 1980) fuel level meters .(Chevrolet nova,Camaro - Pontiac Firebird - Buick regal ,...)

Thanks for the reply

Farshid J.H.