Fuel tube

[1-bad-57]

What is the fuel tube in the cargo area in a 1972 blazer called and what is the purpose? Thanks

[SeventyOne]

You mean the pipe next to the filler neck?

It's a fuel vapor vent stand. 3 vent lines hook to the bottom that aid in tank filling and reduced emissions.

One line will run all the way to the engine bay to the charcoal vapor canister that gets sucked up and burned off by the carb.

It's the only emissions piece on your blazer worth keeping.

[cori 64]

Originally Posted by SeventyOne

You mean the pipe next to the filler neck?

It's a fuel vapor vent stand. 3 vent lines hook to the bottom that aid in tank filling and reduced emissions.

One line will run all the way to the engine bay to the charcoal vapor canister that gets sucked up and burned off by the carb.

It's the only emissions piece on your blazer worth keeping.

Can you get rid of the three vent lines ...and just run the one in the neck?

[SeventyOne]

I dont know why you'd want to. You have the main vent line that runs down with the fuel neck...

But you also have two vent lines that run from the gas tank to the vapor tube, one on each side of the gas tank. This is so that when the fuel sloshes back and forth you always have venting on one side or the other. The third line on the vapor tube, the one in the middle, runs to the charcoal canister under the hood.

At the canister you have three lines. They are all marked on the canister. One leads back to the vapor tube. Another line from the canister is spliced into the PCV line to the carburetor. The last line is a vacuum line that should be hooked up to ported vacuum on the carb.

When you run the engine off idle, the ported vacuum opens a valve on the canister and the engine consumes the gas tank vapors via the PCV line. At idle, the vapors vent out through the canister.

Here's a pic from the factory assembly manual of the gas tank and vapor tube lines:


This is basically a closed system and if you remove the lines as you'll get a gas smell, higher evaporation rates, and maybe a fuel leak depending on how you plug the holes.

[mister.freeze]

my tank only has the one up the fill tube and one on top (some sort of aftermarket 36 gallon thing). If I connect the top one to this tube, with no other lines (no charcoal canister or anything), will the tank fill better and not gurgle out the fill neck so often?

[SeventyOne]

Mr Freeze - I think i need pics to understand what setup you have.

[mister.freeze]

All emissions controls are gone. Tank has filler neck, pickup tube, and 2 other fittings. One of those is the vent to the filler neck. The other used to be a return line from the fuel injection. I now have a carb, so it is just plugged. The vent tube (purpose of this thread) is not connected to anything. Should i connect the currently plugged fitting to the vent tube?

[GM man]

Originally Posted by cori 64

Can you get rid of the three vent lines ...and just run the one in the neck?

Negative. If you don't have the big vent tube you'll have trouble filling the tank.

[GM man]

Originally Posted by SeventyOne

I dont know why you'd want to. You have the main vent line that runs down with the fuel neck...

But you also have two vent lines that run from the gas tank to the vapor tube, one on each side of the gas tank. This is so that when the fuel sloshes back and forth you always have venting on one side or the other. The third line on the vapor tube, the one in the middle, runs to the charcoal canister under the hood.

At the canister you have three lines. They are all marked on the canister. One leads back to the vapor tube. Another line from the canister is spliced into the PCV line to the carburetor. The last line is a vacuum line that should be hooked up to ported vacuum on the carb.

When you run the engine off idle, the ported vacuum opens a valve on the canister and the engine consumes the gas tank vapors via the PCV line. At idle, the vapors vent out through the canister.

Here's a pic from the factory assembly manual of the gas tank and vapor tube lines:
Attachment 1755114

This is basically a closed system and if you remove the lines as you'll get a gas smell, higher evaporation rates, and maybe a fuel leak depending on how you plug the holes.

I installed a 31 gallon tank for a 87-91 Jimmy and used the sending unit with 4 outlets. In addition to the small vent line that runs along with the fill tube, I had a 5/8" vent line that comes off the sending unit. I removed the 3 small vent tubes from the pipe in the diagram you posted, and ran this 5/8" vent tube inside the pipe. I'm thinking about re-installing the charcoal canister but locating it at the back and connecting it to that 5/8" line somehow because I do get a gas smell when the tank is full.

[1-bad-57]

Thanks for the info guys.