[Darin]

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?

 

[260]

If your car has the NA9 evap.emission canister then the non-vented is stock.However chances are you dont so stick with the stock vented cap and dont fill it up to much.

 

[COPO]

It sounds like a vacuum is being created as the tank gets empty. I've been there when my vent hole in the cap was plugged. So yes you need a vented cap and don't fill it to the top. If you leave the non vented cap on then you will also get surging at the carb while driving. I'm supprised you didn't mention that.

Mark