engine and drivetrain Fuel Vapor Return Line?

[devotion]

removed smog from my 76, and have a left over line. From what I can tell it goes from the gas filler neck to the engine bay. I had it marked as "fuel return line" what shall I do with it now that I removed the smog canister in the engine compartment? I dont want it venting to the trunk!

[M3M3]

that canister was not a part of the smog system that had any negative effect on performance.  it just filtered the gas fumes from the atmosphere.  you could have left it in if the canister was still in good shape.

 

others have recreated that same canister functionality in the trunk with the output run out through hole in trunk floor.  you can find the threads on that with a search.

 

early cars vented the tank directly to atmosphere through hole in trunk floor

[jimk]

It's a vent, that's how the air gets in the tank as the fuel is extracted.  It does vent vaporized fuel when the car is standing.  It is supposed to go to the air cleaner so the vapors are burned (it's gasoline that you bought!).

Edited November 25, 2013 by jimk

[Mike Self]

If the charcoal cannister in the engine compartment was removed, leaving a metal line that ends under the battery, you need to plug the line either at the engine compartment end, or at the tank.  Otherwise when you fill the tank gas will siphon out of the tank and dump gas on the ground under the engine.  Not a good scenario.  

 

You can plug that return line nipple at the tank, and then vent the tank from the fitting on the rubber filler neck.  Bet you'll find a rubber plug covering a hole in the metal trunk floor, used to locate the vent line on Euro cars that don't have all the emission stuff.  Just make sure the tank is vented, or the fuel pump won't pump as a vaccum forms in the tank.

 

cheers

mike

[FunkyLaneO]

If the charcoal cannister in the engine compartment was removed, leaving a metal line that ends under the battery, you need to plug the line either at the engine compartment end, or at the tank.  Otherwise when you fill the tank gas will siphon out of the tank and dump gas on the ground under the engine.  Not a good scenario.  

 

You can plug that return line nipple at the tank, and then vent the tank from the fitting on the rubber filler neck.  Bet you'll find a rubber plug covering a hole in the metal trunk floor, used to locate the vent line on Euro cars that don't have all the emission stuff.  Just make sure the tank is vented, or the fuel pump won't pump as a vaccum forms in the tank.

 

cheers

mike

Mike,

 

You are thinking of the fuel return line on the later cars, the one that goes to the charcoal canister is the vent line and if you plug it your tank will no longer be vented, not a good thing.  If you removed the bypass valve next to the carburetor you definitely want to cap that line as you will dump fuel all over the ground but the vent line needs to vent somewhere and it is not cool to vent directly to the atmosphere.

 

The factory system was actually pretty good and you should leave it intact, it allows the vapor to condense in that little tank in the trunk and run back into the tank (less wasted gas to evaporation) and the vapors that do escape go through a charcoal filter that cleans it up some and then it vents through your engine burning up the rest.

 

It is a pretty efficient system that has zero affect on performance so there is no real reason to eliminate it.

 

HTH

 

Lane

[Mike Self]

Hi Lane

It appears that the system on the '76 is quite different from that on my '73.  That vapor return line on my car went from the vapor canister in the engine compartment via a flex hose and mated with the metal line under the battery box; that line then went directly to the gas tank, where it was attached to a nipple on the tank with a short length of hose.  That's the line that peed gas all over the ground the first time I filled the tank after removing the underhood canister/flex line.  No FAQ board then so I had to figure out where the gas was coming from.  I did vent my tank somehow, but that was 20+ years ago and I just don't remember what I did.  But it's been working OK, so it must have been right.

 

Thanks for the clarification.

 

mike

[jimk]

Mike,

The locking gas caps will pass gas (air, I mean).  The ones I have seen are not air tight.  That may have been your solution.

Edited November 26, 2013 by jimk

[darrinos]

I'm wondering if this might be a part of the problem with my '74. I have tried several times to figure out why I continue to get air in my fuel line, resulting in the engine dying, always mind you, in the most inconvenient of places. I have replaced the fuel pump, fuel filter, removed the filters completely, removed the pick-up tube to clean it AND the tank, replaced fuel line, completely removed the pick-up tube and used only a hose as a pick-up....all to no avail as yet. The carbon cannister has not been connected since I bought the car. I'll sure listen to suggestions because I LOVE driving the car. My next step is trying an electric fuel pump with the thinking that there is a (slight) chance that the new fuel pump I got is bad. It's so frustrating because it will sometimes run for days with no problem but then, there it is...no fuel in the carb because I'm getting air again. I can see it in the clear fuel line coming out of the tank and coming from the firewall. Suggestions appreciated.

[roadhog0]

You probably are sucking in air somewhere from the plastic hose. The charcoal canister will NOT affect how the car runs. You can either run new fuel hardline, but since it looks like you already have a late car you can run your fuel lines with the old steel return line (if you dont have a solex.) ALSO if you let the car sit gas boil off, also if you turn it off and it's hot and parked in the sun, again gas will boil off. Happens to me all the time...

[darrinos]

I guess since it's cheaper I'll replace the clear fuel lines first. It's weird though because it had been so darned reliable for so long and now...not so much. Today I went out to mess with it a bit and noticed something. I think the car could probably idle forever and never cause trouble, but when I rev it up a bit and open the secondary on the carb, that's when I start getting the air in the lines. The secondaries open, it sounds good, but then it starts to spit and sputter as if it's not getting enough gas to the secondaries. Makes me think about a float level. It's a new(er) carb, not even a year old yet. It usually won't die after I do this, but won't let me hit the throttle for a bit with out the engine dying. But if I just let it idle, it does just fine. I have a clear fuel filter with a cleanable cartridge inside and I can see air bubbles coming into the filter assembly, though it never goes dry or empty. It's just weird.

[Hans]

So you stuck the fuel hose directly into the top of the tank and still got bubbles?

[Robotin]

you guys are all talking about the later cars. but my '70 has that vapor line that goes from the engine bay to the filler neck. 

 

 

so is it not a return line? what do i do with it if i dont have the stock air cleaner?