71 Dart, Fueltank to crankcase vent as return line?

Fuel and Air Systems

  1. Cope

    Cope Fusing with fire

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    Hi folks, I had a vaporlock issue and would like to add a fuel return line. Problem is my car was.npt fitted with one from the factory.

    Seeing as my car is a 1971 modle and is equipped with the four corner fueltank vent system and fueltank to crankcase vent can I simply use the crankcase vent as a fuel return line?

    If so anything I should be aware of?

    If no how would I go abbout adding a fuel return system?

    Thanks again for the time and advice.
     
  2. roccodart440

    roccodart440 Well-Known Member

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    What size is that line? My return line is 1/2". Feed line 5/8" so whatever size it is should be 1/8" smaller than the feedline using Aeromotives guidelines.
     
  3. 67Dart273

    67Dart273 Well-Known Member

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    Not sure but I think you are confusing terminology. "Crank case vent"

    Doesn't your car did / does have a vapor separator in the trunk?

    That should have a 1/4" line coming from that up to the front of the car.

    "You could" use this for fuel return with a few caveats.

    First that one single 1/4" line IS THE TANK VENT. This means you'd have to do "something else."

    The minor caveat is that line has a little valve near the front end of the line. You would want to cut that out of there

    IF you do this, here's what I'd do. Pull the filler tube out, and weld, silver braze a fitting up high on the filler neck and then duplicate the 69/ earlier vent system.

    This simply is a 1/4" line coming off the filler, going up high in the rear quarter, then coming back down along the filler tube and "open ended" inside the rear frame rail.

    Here

    http://www.forabodiesonly.com/mopar/showthread.php?t=183956

    The early vent system. It's simple and works

    [​IMG]
     
  4. Cope

    Cope Fusing with fire

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    It looks to be the same Dia. as the feed line. Infact both the feed and what im calling crankcase vent run ontop of each other inside the passanger side frame rail.

    If it stops rainning today Im gonna blow air in the line and lissen in the tank.
    I was thinking of using.the Wix 33040 filter with return nipple after my pressure reg and before the carb.

    Is this just a totally bad/wrong idea?

    Thanks again.
     
  5. Cope

    Cope Fusing with fire

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    No vapor seprator in the trunk.

    This is what I had read that got me thinking about this path.

    By Slantsixdan.

    m you're asking about is present on '70 California cars and '71 50-state-plus-Canada cars. '71 was the first year all cars in North America (not just California cars) were equipped with evaporative emission control systems (ECS). This first-two-years system is more complex than the relatively simple '72-up system.

    The '70-'71 setup uses a complicated fuel tank: there is a small inner tank at the top of the main tank and connected to the main tank chamber by a very small passageway, so that the main tank chamber fills up with the secondary chamber still mostly empty. The gas pump nozzle detects a full tank and clicks off, you hang up the nozzle and drive off. Over the next little while, the secondary tank fills up from the main chamber, dropping the fuel level in the main chamber so as to prevent fuel leaving the tank when things warm up and expand.

    These '70-'71 ECS fuel tanks have four vent fittings, one at each corner of the top of the tank. These are brought together in the trunk to a more-or-less vertical vent cylinder leaning against the left wheelhouse — that's what you're seeing. This vent cylinder has five hose fittings: one for the hose from each corner of the tank, and one for a hose connecting to a line that runs up to the right rear corner of the engine bay. it is not supposed to vent into the trunk!

    Inside that vent cylinder, each of the four fittings from the corners of the tank continues vertically, each to a different height. The fitting to the engine bay continues inside the cylinder almost to the top. The idea with the 4-corner venting and the different-height pipes inside the cylinder is that no matter what angle the car is at, in what direction, there will always be at least one vent fitting above the liquid-fuel level, so there'll always be a vapour vent, thus preventing pressure buildup that would force fuel vapours out into the atmosphere.

    The '70-'71 ECS is also unique and interesting in that it uses the engine crankcase to store fuel vapours piped forward from that vent cylinder in the trunk and from the carb bowl. The interface point is a fitting on the fuel pump body on slant-6 cars, or extra fittings on the engine breather cap on V8s. When the engine is started, the collected vapours are drawn off out of the crankcase via the PCV valve. This system does a reasonably effective job of containing the vapours, since the crankcase is well sealed, but it can cause hot start/hot idle problems, since there is no control over when the vapours are extracted from the crankcase. Most of the unburned hydrocarbons wound up out in the atmosphere anyhow, having been first put through the engine (and emitted as black smoke).
     
  6. madmoparmick

    madmoparmick Well-Known Member

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    I did very similar to what you are saying, Cope, on '70 GTX. Holley mechanical
    fuel pump w/out regulator, though. My car had an existing return line, though..
    Put a fitting in fuel supply line near carburetor, and ran a line to existing fuel
    return. Put a Holley main jet soldered closed and redrilled with a smaller hole
    in line as a restriction and had no problems. Later got correct vapor separator
    that mounted on fuel pump as I remember, but homespun bleed worked fine.
     
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