Fire time!!!!!!!!!!!!!

[Sinister Chevy]

This one is driving me nuts! I just replaced my old edelbrock carb with a new one because it was leaking from the '? lower air valve shaft?' (Not sure what to call it but it exits the carb at the rear left.) Now the new one is doing the same. it seems only to happen when the air pressure builds in the tank (even when it has been sitting). Whats the deal? Is a vented gas cap going to cure this? Or is my fuel pressure to high? P.S - I also recently replaced the fuel line and filter.