1967 Dart 273 2bbl odd fuel delivery issue at idle

Discussion in 'Fuel and Air Systems' started by Dana67Dart, Jun 26, 2018.

  1. Dana67Dart

    Dana67Dart Most undignified way to get to Colorado!

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    Has anyone observed the following behavior?

    I have a clear fuel filter ( ya I know I know)
    When the engine is at greater than 1000 to 1500 RPM the fuel filter is completely full
    When the engine is idling the filter will slowly drain till it is completely empty.
    The engine rpm will reduce until a squirt of fuel comes into the filter (but only enough to wet the bottom of the filter)
    The RPM will increase slightly
    then fall off again
    Then another squirt
    The RPM will increase slightly
    then fall off again
    and continues that way till the RPM is raised to 1000 or greater

    I suspect it is the fuel pump, (it was replaced in 2011 but sat for 4 years without running) There is no issue at speed or higher RPM which seems counter intuitive for a bad fuel pump

    Carb was rebuilt 1 year ago, engine runs a bit rich at idle.
    Engine was stock rebuilt in the 80s

    Thoughts?
     
  2. Dana67Dart

    Dana67Dart Most undignified way to get to Colorado!

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    No one????
     
  3. oldkimmer

    oldkimmer Well-Known Member

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    It could be the pump or a pin hole in the fuel line or the sock in the fuel tank could be plugging up or maybe even the fuel filter is plugging up. Kim
     
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    • oldkimmer

      oldkimmer Well-Known Member

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      By the way, the fuel filter wil never be always full, it varies a lot. Kim
       
    • Dana67Dart

      Dana67Dart Most undignified way to get to Colorado!

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      New oe puckup, no fuel leaking anywhere, filter is see through and doesn't restrict flow at higher rpm. I would have thought that the only time the filter might be less than full would be at high rpm assuming the pump couldn'keep up.
      Its the drop in level with a resulting drop in rpm till the filter starts to fill again that has got me baffeled.
      Fuel pump is 7 years old and easy to change so i might do thst first.
       
    • Dana67Dart

      Dana67Dart Most undignified way to get to Colorado!

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      Oh and thanks for the reply Kim. 20 something people have looked at the post and your the only one to reply
       
    • oldkimmer

      oldkimmer Well-Known Member

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      No problem. Hopefully this helps. It may not leak fuel, but it can suck air. Kim
       
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      • Dana67Dart

        Dana67Dart Most undignified way to get to Colorado!

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        Good point.
         
      • 4spdragtop

        4spdragtop FABO Gold Member FABO Gold Member

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        Yeah diaphragm in pump may have pin hole.
        Doesn't stumble at all?
        Could you hook a Mighty Vac to pump to test?
         
      • AJ/FormS

        AJ/FormS 367 FormS clone 3.09-1.92-1.40-1.09-.78od 3.55s

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        Fuel pump output test
         
      • Dana67Dart

        Dana67Dart Most undignified way to get to Colorado!

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        Nope, at above idle it is fine. at idle it drains the fuel filter then sputters fuel into the filter enough to keep the engine running but at a lower rpm.

        Ill test the fuel pump pressure and flow and report back
         
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        • Dana67Dart

          Dana67Dart Most undignified way to get to Colorado!

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          Some video of the fuel filter.

          It only seems to do this when the engine heats up. The fuel filter was between 140 and 156. A form of vapor lock????



           
        • famous bob

          famous bob mopar misfit

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          Try running the filter standing up , if u got room.
          Pump is suspect !
           
        • Dana67Dart

          Dana67Dart Most undignified way to get to Colorado!

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          Isn't it odd.

          I have to assume that there is pressure in the filter preventing additional fuel from coming in and once the float lowers enough I suspect the gas vapor pressure inside the filter is relieved and fuel flows. I pressure tested the pump and got 8.5 lbs and it held after the engine shut off.
          The float needle is sealing as there was pressure in the lines when I separated the filer from the lines.
          The engine was cold at the time I tested the pressure so it might be a heat related issue. I'll recheck the pump pressure when it is hot and with a "T" in the line after the filter to see what the running pressure is.