I have a 74 Challenger that I have swapped in a 440. Last winter, I installed a Holley Sniper. I used the Spectra efi tank. It has the four vent tubes on the top of the tank that connect to a fuel separator and then to the engine bay just like the original. The evap canister was removed many years ago. It has been vented to atmosphere since then. It worked fine. About a month ago, I started smelling gas fumes after driving some distance. I found that the vent line for the evap system was spitting fuel.

I figured that I could just run a vacuum line from the evap line to the throttle body and that would take care of it. The car ran OK until the next fill-up. It started sucking so much fuel through the line it was extremely rich and wouldn't hardly run.

Plan B. I mounted a small container and just vented the evap line into it to catch the fuel. That worked somewhat for a while, accumulating a small amount of fuel which I would dump into the mower.

Last night, I took the car out for a drive. I filled the tank and drove about 20 miles. When I pulled the car in the garage and shut it down, I could hear a gurgling sound. I checked the overflow container and it was almost full. I opened the fuel cap and I could hear pressure escaping and the gurgling quit.

I am using the original fuel cap that was on the car new. I am the original owner, so I know it's original. I think that cap is supposed to hold a small amount pressure, but vent the excess.

Has anyone else experienced this? If so, what did you do to fix it?

So you used the stock vapor separator it sounds like?

The stock system vented through the charcoal canister. The gas cap is sealed. There are some check balls inside the stock vapor separator. I wonder if one of those is rusted closed. I'd remove the vapor separator and soak it in EvapoRust. You can block 3 of the 4 inlet ports with your fingers, then suck/blow through the other one and feel the check balls moving around. They only allow air flow in the middle of their travel. If you suck/blow hard, you will push the ball to its seat and it will block the air flow.

You could run a vented gas cap also. That would solve the problem.