Gas tank pressure

[Jolby]

I am wondering what is the best fix for excessive gas tank pressure. It actually floods the carb and leaks down onto intake manifold. I hooked up my under bed tank and capped off unused lines. Can I solve problem with a different gas cap and if so which one? Do I need some type of tank vent or canister? The filler that I have uses the same cap as the stock tank but with that cap the pressure is high, large whoosh when uncapping.