might be a crazy question.

I just picked up a 70 Challenger with a 360. Car does not want to run with a non vented gas cap. Take the cap off and it will crank and run fine. I have not tried driving it like this though. Does this make any since?

If there is no good vent for the fuel tank it will likely have that problem.

The pump can't draw fuel from a vacuum.

Every 1971 car had an evaporative emission system and a non-vented gas tank. Yours is probably plugged or capped off or something. Fix it.

R.

Mine is a 70.. No concern here about emissions..

1970 cars made in the LA Plant also had some of those emission "extras".

I did not replace the return fuel line on my 1970 Cuda when I stripped the undercarriage last year and so I "vented" my cap and used a PCV-like valve to let air go into the empty line instead of plugging it.

If I had plugged it and not opened the cap I would have been in the same boat.