Vented fuel tank building pressure

[BigDen1947]

I recently purchased a 1972 Plymouth Cuda that has been restored. The car is numbers matching and has the original 340 ci engine. There is a Holley Sniper fuel injection on the engine. The a new Holley vented gas tank was installed and the Holley w/ internal fuel pump has return line from the Sniper to the tank. Recently, after driving the car in hot weather I heard a high pitch sound coming from the gas cap and when opened there was a lot of pressure. Once relieved I put the cap back on and I could hear a trickling noise in the tank. Open the cap it stops, put it back on and it continues for several minutes. My cap has pressure or vacuum on the inside. I ordered a replacement but it hasn’t come yet.

Any help will be appreciated.
Thanks

 

[Chryco Psycho]

Clearly the tank is not vented , 70 was the only year with a vented cap from the factory but that would solve the problem , I don't recall if 72 had the 4 extra lines from the tank into the separator but it would have either vented to the breather on the valve cover or into a carbon canister in later years but there would be a line running forward to the engine bay from the factory which may have been eliminated .

 

[BigDen1947]

Clearly the tank is not vented , 70 was the only year with a vented cap from the factory but that would solve the problem , I don't recall if 72 had the 4 extra lines from the tank into the separator but it would have either vented to the breather on the valve cover or into a carbon canister in later years but there would be a line running forward to the engine bay from the factory which may have been eliminated .

The tank is new from Holley it has vented fill line with a hose on top. I’m not sure if the hose has a filter with a built in check valve or not.

 

[BigDen1947]

The tank is new from Holley and it has a vented filler pipe w a hose running above the tank top. I’m not sure the hose has a check valve on top.

 

[cuda joe]

that vent has to be clogged. i had the same problem with my 71 I opened the separator in the trunk and found one line that had rust on the tip

 

[Steve340]

Hopefully the new cap will fix the problem. Check the vent tube is not restricted.