Hello I have a 1968 Pontiac firebird with a 454BBC chevy. I have all new stainless steel 10 gallon tank along with new straps and filler neck, 3/8 stainless steel fuel line (one fuel line going to the carb no return line. I have a holley red electric fuel pump and a holly 750 carb with a pressure regulator 4.5 pressure at the carb. My question is I get a alot of pressure coming from the tank when I remove the vented fuel cap. I did purchase this cap from classic industries and it is the cap that is called for a 1968 firebird. but i get alot of pressure when i take the cap off the tank esp if the fuel guage is low (I know that gas expands) but i think the cap is not doing its job at venting the fuel tank properly. the pressure is soo bad that when i try to take the cap off it litteraly shoots about four to five feet away from the tank and I also get a fumes smell in the vehicle esp if i make a right or left turn and when the fuel is low I am guessing due to the high amount of fumes and pressure in the tank. My question is has any one here had this situation before or does anoyone here in this forum have a part number as a replacement for the OER cap that I bought from classic industries. I have tried Napa Pep Boys Auto Zone Advanced Auto but they give me a cap that does not work I hope that someone in here has a part number that might help me in my situation thanks