I have only recently begun to daily drive my '70 that I reacquired. When I owned it the first go around I had a vented locking gas cap. I remember filling up back then nailing the accelerator and leaving a trail of gas. (yes the cap was on) It currently as a stock type unvented cap. Today when I went to fill it up the fumes liked to blow the cap out of my hand. Which type of cap vented or unvented is the right choice?