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Fuel Tank Vent

7304 Views 13 Replies 6 Participants Last post by  Neil Martin
Hi All:
Upon getting familiar with my fuel system, i have discovered that a previous owner had removed the fuel tank vent in my 76 spider. The vent line had been disconnected both at the vent and the breather pipe on the air rack.

I'm looking to replace or fab a replacement vent as the part seems to be NLA. HAs anyone found an equivalent replacement? Part number please. I went to NAPA and they just shook their head in disbelief that I was asking them such a question.

As somebodies wisdom (for better or worse) directed them to remove the part in the first place, i'm interested in knowing what difference it will make in engine performance. Can i go without it? Right now the vent into the vapor tank has a screw strategically inserted into the opening or else the trunk becomes a fume bomb.

your help is appreciated. Thanks
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on my 74, the tank vents with a small hose to the back of the engine. there is a steel tube along the top of the intake manofold, then a small plastic tube to the fitting where the hose to the vapor seperator connects. I guess it is supposed to suck air from the filter boxthru the vapor seperator system. when the vapor seperator system plugged up, my tank would "whoosh" when I removed the gas cap. I think the hose is green.

You're probably only going to be able to get salvage parts. Call APE and see if they have it. Do you have the diagram of all the parts you need and the routing of the vapor hoses?
Hoses are not the issue. Thats easy. All the fuel system diagrams i have show a tank vent in the trunk connected between the vapor tank and the breather line leading to the tube over the air intake manifold. Other than a schematic i don't have a spec for this vent. I know it lets air into the system, not out so it is a check valve arrangement.

I could probably make one but i dont know what spring pressure i need to make the check valve operate under the vacuum from the vapor line.
Not much. Just over atmospheric, I would imagine.
Im not sure how much of your vapor tank hoses/check valves have been gutted, but there is a steel check valve one, which holds back any fuel from spilling freely and subsequently causing a fire in case of a vehicle turnover. Is this one missing? If so, you're at risk for this.
I'm attaching a diagram of the part in question. It is the inline valve under the 22. I assume it prevents the tank from drawing vacuum so the valve hould open to let in air if the pressure in the tank drops below atmospheric. I am also ssuming that under operating conditions the tank will be at a slight positive pressure.
A picture of a real live one would be appreciated. thanks


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Here's from a 74. I'm assuming the S3 Spiders are similar.


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Pretty simular, with about the only significant addition in the S3 being the check valve after the one way breather valve to prevent fuel spillage in the event of reversion and the charcoal canister behind the right front wheelwell.
Bingo!!! Thanks Roadtrip. Now, where the hell do I find one of these? I wonder if a PCV valve will do the trick.
Ahh, what charcoal canister? and, is the check valve between the vent and the engine or vapor tank and engine?
Yours being an S2, I'm not even sure those items would be on your car.

However, if the were, the check valve on the engine side of the vent and the charcoal canister would be behind the right fenderwell behind the panel at the back of the wheelwell.

This thread has a schematic of the S3 system so you can compare differences to the above one.
Roadtrip, another thought. In the picture you show the vapor line returning to the engine. This is a little confusing because i think it connects to the metal tube across the air intake manifold which goes into the valve cover. So the fuel vapour vents into the valve cover? I took the tube off a few weeks back and it was blocked so i cleaned it out with a wire, got the rust off and repainted it. When I put it back on the car with the one end open, steam was coming out as the engine was running. If this is a positive pressure vent, how would vapor get sucked into the engine? To me it looks like it would push into the vapor tank.
Am I totally off track here?
its supposed to get filtered air from the airbox thru the vaor seperator canister.
Forgive me for bringing to life an old thread, but I could not find a response to "where to locate the one way check valve shown in the picture in post #8. Or is this unnecessary in a 74 S2?
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