Gas tank venting issue 1972 Roadrunner

[kcracegirl]

We have a 72 Roadrunner we are having fuel venting issues. We noticed there are times the fuel filter get sucked dry, then the car runs rough, or dies, then the filter will start filling back up and we see bubbles. It is a clear filter that is between the fuel pump and the carb. The gas tank has 4 vent tubes at the top of the tank that are vented into a vaporizer canister. We no longer have the charcoal canister so how do we properly vent the four vent tubes?

 

[poly3521]

Sounds like your gas cap is shot. They're designed to vent the tank so it doesn't build too much positive pressure, and pull air in so you don't have too much negative pressure. Yours sounds like the latter, it doesn't like to open. As far as the vent goes, my '71 has a 3 nipple breather on the valve cover. 1 nipple is for the line from the vapor tank out back, 1 nipple connects the air cleaner, and the last nipple is for the carb bowl vent. 72 had a different breather, the vapor tank and carb bowl vent went to the charcoal canister. On '71s, the crankcase acted as the charcoal canister, and thanks to the EPA, that changed in '72.

 

[72RoadrunnerGTX]

Early ‘72’s used the fuel tank and fuel tank vapor separator from ’71, larger expansion/vapor separator tank mounted in the driver’s side rear wheel well. Beginning April 1 ’72, the system changed to a smaller fuel tank vapor separator mounted above the differential, front of the fuel tank. The four fuel tank vent lines should be connected to the fuel tank vapor separator, in turn it is connected to a hard line running forward to the engine compartment. If the charcoal canister has been removed and you are not planning to restore it, I would find a ’71 three nipple breather cap and connect it there. The line is the tank vent and should not be plugged off, or left open in the engine compartment. The original fuel tank system did not vent through the gas cap, the cap should have an over/under pressure relief valve but not vented.

 

[kcracegirl]

I am going to check the four vent tubes on the gas tank and on the vapor separator. If they are not plugged up and I reconnect my four hoses from the tank to the separator can i take the rubber vent hose on top of the separator and run it to the rear of the car and cap it with a small fuel filter so I dont vent something into my tank. Thank you for your help.

Early ‘72’s used the fuel tank and fuel tank vapor separator from ’71, larger expansion/vapor separator tank mounted in the driver’s side rear wheel well. Beginning April 1 ’72, the system changed to a smaller fuel tank vapor separator mounted above the differential, front of the fuel tank. The four fuel tank vent lines should be connected to the fuel tank vapor separator, in turn it is connected to a hard line running forward to the engine compartment. If the charcoal canister has been removed and you are not planning to restore it, I would find a ’71 three nipple breather cap and connect it there. The line is the tank vent and should not be plugged off, or left open in the engine compartment. The original fuel tank system did not vent through the gas cap, the cap should have an over/under pressure relief valve but not vented.

 

[poly3521]

Early ‘72’s used the fuel tank and fuel tank vapor separator from ’71, larger expansion/vapor separator tank mounted in the driver’s side rear wheel well. Beginning April 1 ’72, the system changed to a smaller fuel tank vapor separator mounted above the differential, front of the fuel tank. The four fuel tank vent lines should be connected to the fuel tank vapor separator, in turn it is connected to a hard line running forward to the engine compartment. If the charcoal canister has been removed and you are not planning to restore it, I would find a ’71 three nipple breather cap and connect it there. The line is the tank vent and should not be plugged off, or left open in the engine compartment. The original fuel tank system did not vent through the gas cap, the cap should have an over/under pressure relief valve but not vented.

Thanks for clarifying. I was trying to say say that, just didn't coe out that way.

I am going to check the four vent tubes on the gas tank and on the vapor separator. If they are not plugged up and I reconnect my four hoses from the tank to the separator can i take the rubber vent hose on top of the separator and run it to the rear of the car and cap it with a small fuel filter so I dont vent something into my tank. Thank you for your help.

If the line to the charcoal canister is still there, run it to the air cleaner or breather. Running it to the back isn't a good idea. It's a low pressure area when being driven and the vapors Could be drawn out and ignited. It's safer to vent the vapors to the engine. That's the way the factory does it, even today.