Originally posted by strokerchevyII
Should the fuel cell be vented?
Absolutely. The fuel cell should have a vent line run from the top of the cell back through the floor venting under the car and it should be equipped with a anti roll over valve. For now try running the engine with the cap off to see if that solves your problem. Even if it doesn't install a vent in the tank.
In the photo below you can see a typical fuel cell installation. The braded stainless steel vent line exits the top of the tank and runs down through the floor. The fuel outlet is at the bottom center of the tank and is also braded stainless steel.