Gas tank ,fuel line vent tube?

[Daves72'GMC]

I Have a 1972 gmc 3/4 that I'm restoring and where the 2 fuel lines come from the fuel tank and go through the cab floor, one line is the big one which I know where it goes ,but where does the smaller one go(where does it hook up too?)? I believe it's a vent line. Thank you everyone.Dvae

[JimKshortstep4x4]

The smaller line is a return line and connects to the fuel pump. (Your fuel pump on the 72 should have an extra outlet on it which is the same size as the return line).

Jim

[Daves72'GMC]

I put an edlbrock fuel pump on and it doesn't have the vent line on the fuel pump, so what do I do with the vent line coming from the fuel tank? Thank you

[clay68c10]

I'd plug it. No need for it with the aftermarket pump.

[Green Machine]

If you plug it be sure to run a vented gas cap from an earlier year. If you don't you will either stave engine for fuel or colapse the tank.

[dwaite72lnghrn]

Yep you will definitly have to plug this line or when you fill the tank it will syphon fuel out onto the ground.

[Daves72'GMC]

The gentleman that is restoring my truck ,said he would just run a hose next to the frame rail with some kind of valve at the end,so it would vent. Does this sound fine .Would it just be better or easier to put the stock type fuel pump back on ,so I don't have to mess with the vented cap. I'd like to keep the origional cap on. Thanks guys for all of your help.Dave

[cdowns]

the original vent goes up into the rear passenger door pillar then down thru th fllor up to the charcoal canister i've always eliminated the canister and had the rubber hose along the frame rail there is no chance of it siphoning out becauce of the height of the vent loop i've never seen a gas pump with a return line on the 3 71-72AC trucks i've had

[dwaite72lnghrn]

I don't think a check valve on the end of the line that vents air both directions will stop the fuel from dumping. My tank lines follow the same path from the tank to the fuel pump. There is no high arch in the hose. When I changed over to electric pump I left the return line there with a loose hose to the other line( rerouted new lines) after the tank was filled and it sat the fuel would dump from the line, I then clamped them tight so it wouldn't leak. If you run an extra hose up high enough like the other trucks then it would be ok as the fuel wouldn't go up that high blocking your vent.