Gas tank vent line puking fuel

[wilkin250r]

I have a 72 with two lines coming from the fuel tank, routed into the engine bay. One is routed to the fuel pump, the other is just hanging out with some sort of breather cap on it. I am assuming it is a fuel vent line (perhaps that assumption is my first mistake).

Problem is, if I fill up the fuel tank beyond about 3/4 full, fuel will begin to flow out of that vent line. Coincidentally, the end of this vent line is mounted at a height I'd assume to be right around 3/4 height of the tank. SO it would appear that as soon as the fuel rises above the end of this vent line, it becomes a drain.

I'm sure that's not normal. The knee-jerk reaction would be "just mount the breather end higher than the tank. Problem solved!" That's not a solution, that's a band-aid. I want to actually SOLVE the problem.

So educate me. Those that have vent lines on their tanks, where are they routed to? Or am I mistaken and this ISN'T a vent line at all? If it's not, then what the heck is it?

[sick472]

You should have three lines coming from the tank on a 72. One for feeding the fuel pump, one for return from the fuel pump, and the last one would originally be hooked to a charcoal canister under the hood which would be the vent.

3/8"=Supply,
5/16"=Vent,
1/4"=Return

This thread might help you out a little...

http://67-72chevytrucks.com/vboard/s...d.php?t=662158

[LockDoc]

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If the charcoal canister is no longer there cap that line at the tank, put a vented gas cap on it, and call it a day....

LockDoc

[wilkin250r]

Maybe that's the answer, it's supposed to be the return line. But I don't have a return plumbed up, because it's not the original fuel pump (because it's not the original engine). My fuel pump doesn't HAVE a return. Just two connections, an inlet and an outlet.

[demian5]

Originally Posted by LockDoc

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If the charcoal canister is no longer there cap that line at the tank, put a vented gas cap on it, and call it a day....

LockDoc

That's such an easy thing to say...

Im on my 4th cap in a month. I have a 70 with non vented tank. I get two results from them, either too much pressure in tank (that the cab smells like fuel and the gap about blows out of my hand when removing) or fuel spills all over side of truck when I make a hard right turn.

[LockDoc]

Originally Posted by demian5

That's such an easy thing to say...

Im on my 4th cap in a month. I have a 70 with non vented tank. I get two results from them, either too much pressure in tank (that the cab smells like fuel and the gap about blows out of my hand when removing) or fuel spills all over side of truck when I make a hard right turn.

That's only because some of the new caps are really crappy. Obviously the non vented one is working good though..... What brand are you using. I have had pretty good luck with Stant caps. I have replaced the rubber seal and brass backing plate on a couple of originals with good luck.

LockDoc

[Andy4639]

You may want to consider a late model charcoal canister to hook to it and take care of the smell. They are cheap enough at the local yards and install it under the battery as factory out of sight. Are you could use the factory one if it's still there and go to Walmart in the fish area and buy a couple of bags of charcoal to rebuild it.

[kenn]

Hello, Obviously the return line to the tank is clear so if your using a mechanical pump you could change to one with a return connection.

[wilkin250r]

Looks like it's time to pull the seat and get a really good look at things.

I definitely do NOT have a charcoal canister under my battery, nor do I have the lines running a high loop up the passenger side door frame. But I could probably fabricate them if they seem to work. It sounds like the vented gas caps can be slightly problematic with a full tank of gas.

Anybody have an original charcoal canister, can give me some direction (or pictures) for hose routing?

[wilkin250r]

Well, the story I heard was that some 70-71s had vent lines, but all 72s had them. Either that is not the case, or this is not the original fuel tank because I do NOT have the vent line that runs up the passenger side frame rail.

I do have two lines on my sending unit. I believe the second one is a return line?

It looks like the plan is to cap that return line. Can somebody give me a link or part number to a vented gas cap?

[Sheepdip]

Originally Posted by demian5

That's such an easy thing to say...

Im on my 4th cap in a month. I have a 70 with non vented tank. I get two results from them, either too much pressure in tank (that the cab smells like fuel and the gap about blows out of my hand when removing) or fuel spills all over side of truck when I make a hard right turn.

Take the cap that only vents inwards and right in the center is a little hole, in there is a one way check valve, take a 1/8" drill bit and go through the motion to drill it out. You actually will spin it (not drill it) and destroy the one way action. When you can blow back through it your done.

Just did one 2 days ago

[GASoline71]

Originally Posted by wilkin250r

Well, the story I heard was that some 70-71s had vent lines, but all 72s had them. Either that is not the case, or this is not the original fuel tank because I do NOT have the vent line that runs up the passenger side frame rail.

I do have two lines on my sending unit. I believe the second one is a return line?

It looks like the plan is to cap that return line. Can somebody give me a link or part number to a vented gas cap?

See that dimple in the tank over on the passenger side? That is where the original fuel tank vent line would come out of and go up into the passenger side C-pillar, and back down the side of the tank. Look at my stock tank setup in my 1972 GMC C1500 in the linked post below.

http://www.67-72chevytrucks.com/vboa...&postcount=313

I also have the return line capped off at the sending unit.

Gary

[wilkin250r]

Originally Posted by GASoline71

See that dimple in the tank over on the passenger side? That is where the original fuel tank vent line would come out of and go up into the passenger side C-pillar, and back down the side of the tank. Look at my stock tank setup in my 1972 GMC C1500 in the linked post below.

Yes. And if I were a brave man, I would pull the tank and drill a vent line.

But I'm not that brave.