Insert in Gas Tank Vent Pipe

It allows a constant pull of fumes from the fuel system by the engine when running, but because the hole is so small it doesn't create enough vacuum to be a vacuum leak or pull liquid fuel, also it prevents excessive vacuum being applied to the vapour system according to the service manual.

later
Tim

 

One last question on this issue, I promise, is that section of hose at the cannister (in the engine compartment) or at the vapor separator?

Thanks.

Len

 

Connects the vapour separator under the back seat to the emissions line that runs up front to the cannister. That would put it right in front of the fuel tank. It is the fourth line off to the side by itself out of the vapour separator.

later
tim

 

Thanks. Now where can I find one?

 

Any 71/72 machine will have it, including the big cars...

later
Tim

 

Len I am in the same boat as you because if I had one it is about 60 feet down in a land fill by now as I replaced all my line years ago. Never noticed that thing only old brittle rubber lines.

 

Tim , how big is the hole in that thing I may try and make one. And which end of the rubber does it go in. We will drive you crazy with all these questions but you showed us that #@%!$ picture!

 

I'm not sure, nothing to measure it with at the moment, I would guess .045-.050" or so. I don't think it would matter which end of the hose it goes in, as long as its there.

Would be pretty easy to make out of plastic or aluminum. I can get you better measurements tomorrow.

later
Tim

 

Guys,
71 & 72 cars had no rubber mat above the gastank. That stopped at the end of the 70 model year. Check your assembly manuals, it shows no mat.
Duane

 

I checked th 71 assembly manual that hose assembly has a part #. I checked some of the online GM parts houses and it appears to be discontinued. #3993625. Tim measurements would be great. MAybe a drill bit coud measure the orifice.

 

Is this vent really a necessity? o No:

I just left my lines extra long, kinked an "S" in them and then hooked them down tight to the body.

 

The tank has to be vented somehow. For '68-70 there were two tubes inside the tank, running above the fuel level, to opposite corners. The idea is that no matter what angle your car is parked at (think: San Francisco), at least one of the tubes will be above the fuel level.

Venting the tank is necessary, first, so the pump doesn't have to fight a vacuum, and second, so that changes in temperature and atmospheric pressure don't push fuel out.

The plastic thingy is advantageous in that if fuel is splashed or pushed out one tube, it will likely return through the other tube instead of spilling on the ground (or exhaust!). It also is supposed to have a small foam plug in the end, which helps keep dirt and water from getting sucked into the tank.

You can vent your tank with just the hoses (no plastic thingy), but you'll miss out on those benefits.

On a related note, I've heard numerous stories of people installing a modern reproduction gas tank and then having problems with fuel leaking out the vent tubes as the temperature changes. My interpretation of this is that the quality control for these tanks must not be that good, and one or both tubes are likely submerged in the fuel instead of staying above it.

 

Dee,
Vent is not necessary. Your hose set-up will work fine.

 

Thanks guys! :TU: