I was discussing the issue of a return fuel line with a buddy who is rebuilding a 67 Firebird, and we had some questions.

My 68 FB was originally a 350 car w/o A/C, and I believe a California car. It came with a return fuel line. I have since replaced the fuel system and added a 400 motor. The new fuel system does not have a return fuel line. Should the gas cap be vented or non-vented? Which cars came with vented or non-vented gas caps. Were these dependent on whether car had or did not have a return fuel line?

Will not having a return fuel line cause problems?

Thanks,
Chris

Chris, All gas tanks have to be vented. Some are vented with a line from the fuel filer tube(69) and some use a vented gas cap(67). Newer cars vent back to the motor to re-burn the vapors.
Your car will be fine without a return line if you have the right fuel pump for no return.
Must be because of being a CA car.

I changed the fuel pump and sending unit to a single line setup.

So the 68 system should have a vented gas cap?

Thanks,
Chris

Fuel return line and vented cap are part of two different functions.

If your car has a separate vent tube attached to the fuel filler neck area then you need a non-vented cap. If your tank does not have a vent tube then you need a vented cap. To be sure, drive the car then remove the fuel cap. There should be no suction when you remove the cap.

Pardon the hi-jack, but I've seen several questions now from people wondering whether or not their cap should be vented or not.

It begs the question: what happens if you should be using a vented cap, but aren't? Aside from "suction when you remove the cap", does it cause other problems? Could it cause starting problems (perhaps because the gas is "vacuumed" back into the tank)?

If you need one and arent...you can encounter problems , like blowing your sending unit gasket if you park the car with full tank in hot weather , gas expands.

Bjorn has a point, petrol does expand as all liquids do when heated. A non vented tank would make it hard for the fuel pump to operate correctly.

nonvented for the 67 and vented for the 68.