I have this problem.. on hot days, with not alot of gas, my fuel tank builds up a ton of pressure. The car starts to run bad, and I have to pull over, and remove the gas cap. I get this huge "woosh" of extremely flammable gas vapor.
I have a vented gas cap.. I've tried different gas caps. This leads me to a question...
I think when I was restoring the car, I read somewhere about an activated charcoal vent line that goes from the tank to the atmosphere.
Am I missing a vent line? Does this item I am thinking of exist?
I'd like to remedy this pesky problem..

Matt

Drill a small hole in the cap.
this will vent the tank.
what year is the car?
my 71 had a vapor canister in the upright portion of back seat.
it was leaking, every time we put gas in the tank ,it would vent into the car.
made it tough to light up.

I have a 72, simular to a 71. I have a vent running from the tank to a canister under the hood, and back to the tank. the canister is run to the pcv in the rocker cover then to the carb.

What year is your car?

Its a 1970. I don't run a PCV setup. Whats my best option here?

Matt

Is there vent lines on a 70 tank? The tank has to be vented somehow, you'd think...

You don't have to run it to pcv, just run it to the canister, then to open air, I'd think as long as it went thru the charcoal, it'd be alright.

Had a 71 that my wife wrecked, put a gas tank in from an older Olds, didnot hook up the vent line to the canister, just crimped it off, thinking was that I didn't want water getting in the tank. Had the exact same problems your having. Either vent the cap as already suggested. or make SURE the vent line is in good shape and connected up to the canister. No need for charcoal if you don't mind the smell of gas fumes.. :cool:

I have the vent coming in on the upright of the backseat too on my 71, anybody know why GM vented it inside the car? why not just above the gas tank or somewhere so it atleast doesnt get inside.