Vapor Lock question

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  1. Petty Blu 72

    Petty Blu 72 Active Member

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    After a short drive, say 3-5 miles. I open the gas cap and get quite a lot of air rushing in the tank. Could I soon get vapor lock? Why is the cap not allowing air to replace gas? Could it be plugged? Is there a way to check it?
    Should I drill a small pin hole in the cap to allow air to come in tank?
    Any thoughts?:glasses7:
     
  2. tekslk

    tekslk Well-Known Member

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    I would try that first and if it fixes it maybe a new gas cap. Or be happy with it.
     
  3. ntsqd

    ntsqd Well-Known Member

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    Shouldn't a car of that era have a simple tank vent? The vent on my'65 is attached to the fill neck near the top. I'd check that for being plugged before doing anything else.
     
  4. Daves69

    Daves69 Well-Known Member

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  5. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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    No. These cars do not and should not use a vented cap. All that will do is throw gas all over the side of the car. All these cars are vented by means of a small tube attached near the top of the filler tube in the trunk. Pull that tube loose and make sure it's clear. It simply goes down through the trunk floor gasket, and "open ends" inside the rear frame rail on 67 / newer cars, on older cars not sure where it ends



    CORRECT!!!!
     

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    • Bad Sport

      Bad Sport HALF A BUBBLE OFF Staff Member FABO Gold Member

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      No such critter on my car. Mine has a vented cap.
       
    • 67Dart273

      67Dart273 FABO Gold Member FABO Gold Member

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      Somehow I got the impression we were talking about a 65? Then I look at your screen name??????????? So what, a 72?................................?

      This is a different animal. This originally had the evaporative emissions 'stuff' and a so called "pressure vacuum" cap. Have you modified the tank system? What did you do with the 1/4" line coming up to the front?

      How it works is in the shop manual:

      http://www.forabodiesonly.com/mopar/showthread.php?t=244981

      http://www.forabodiesonly.com/mopar/showthread.php?p=1969591363

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

      [​IMG]

      [​IMG]

      [​IMG]
       
    • Petty Blu 72

      Petty Blu 72 Active Member

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      I will have to look into this further. Mine is by no means stock. Wonder if that changes things? I have an electric fuel pump near tank, and very heavy duty and rather large fuel lines running to carb. The car was never meant for long rides, but built for dragging. The gas cap is painted the color of the car.
       

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    • 70 DUSTER CRATE

      70 DUSTER CRATE Well-Known Member

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      You're not getting vapor lock, you're getting more of a vacuum lock.
      It's got to effect performance.

      Does the inside of your cap look like the picture that 67Dart273 sent ?

      Take your cap and line the inside with a paper tissue, then put your mouth on that tit and suck on it.
      Do you get any air ?

      My 2 cents.

      That's a nice looking shifter. What Brand is it ?
       
    • 67Dart273

      67Dart273 FABO Gold Member FABO Gold Member

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      Looks like a Winters which is what a Cheetah really is, down underneath

      You very well could have a different year tank in the car, that is, anything is possible.

      Only thing I know at this point is to get under there and take some photos of the tank area both underneath and in the trunk to see if we can see what's still there.

      If this were mine, I'd drop the tank, plug anything left over from the original vent, and braze a fitting into the filler tube and convert it to the 69 / older style.

      I'm not exactly sure when Ma changed all this stuff

      In 72, you should have a "big can" (vapor separator) sticking up in the trunk with several hoses / tubes going to it. Look at the diagram I posted. In 73, Ma seems to have gone to the later 73/ 74 type which had "all that" in the tank

      In opposition to others on here I would NOT vent the cap. This is a great way to get gas splashed all over the side of the car.
       
    • ntsqd

      ntsqd Well-Known Member

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      Yeah, gotta agree, do not vent the cap.

      Check the venting, if you're making some HP you may need to increase the size of the vent. Where exactly to put it depends on too many variables, but if racing is in the mix then have a good look at their rules book. A series that I crew in requires that there always be a part of the vent line that is above the fuel level no matter how the vehicle is rolled.

      I like to put one of the plastic bodied cheap fuel filters in the end of the vent line hose. Keeps any road grit from getting in and either plugging the vent or getting into the fuel itself.
       
    • MoparPhil

      MoparPhil Well-Known Member

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      The electric fuel pump can change things especially if you have changed from 5/16" to 3/8" or larger fuel lines. The new 3/8" sender unit on mine has an additional vent line to which I built and attached my own vent system using coiled aluminum hose and an inline fuel filter. The coils keep the fuel from sloshing out. Some add a one way valve so fuel can't get out in case of a rollover. It works great and the fuel flows perfectly.
       
    • jonnydart440

      jonnydart440 Well-Known Member

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      First off, nice car. Secondly, long story short, being a 72, u definitely had some sort of charcoal canister originally, which means u have more than just a fuel line coming out of the tank. I would follow those other lines, most likely someone deleted the canister and figured they should just plug the lines. U need to leave at least one open as a vent. If u drive 3 miles, shut the car off and open the cap and release a vacuum than u have very little if any venting at all.
       
    • Petty Blu 72

      Petty Blu 72 Active Member

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      Think I am gonna vent the filler neck and run a hose along the neck and down under near the frame. Sort of like this one I found on the net, only difference it that it will connect into filler neck near top.
      Thanks for all the knowledgeable info!
       

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    • ntsqd

      ntsqd Well-Known Member

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      Place loop in the vent line that goes as high up above the fill neck as there is room for under the package tray. That is the way that my '65 was done by the factory. Makes any liquid fuel have to climb that much higher in order to spill on the ground.
       
    • 67Dart273

      67Dart273 FABO Gold Member FABO Gold Member

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      This is exactly what I posted earlier. The only reason the factory changed it is because of the evaporative emissions stuff came along in 70/71. If you have the means and skills to do so, that is what I'd do.
       
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