Preasure building up in my Gas tank (72)

[72 Super]

My gas tank in my 72 4x4 keeps building up pressure. Everyday I remove the cap to relieve the pressure. It also has a pretty strong fuel smell when you open the door. I would assume this is venting issue. It has the correct 72 vented tank in it. It doesn't have the original gas cap, Is there a way to tell if the cap is vented versus non-vented?


Thanks,
Ray