Holley Experts: Stumbling?

Discussion in 'Fuel and Air Systems' started by doc540, May 1, 2018.

  1. doc540

    doc540 Well-Known Member

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    Everything has been copacetic for over a year, but recently my Holley 390 on the Slant has started stumbling right "AFTER" acceleration.

    It's not hesitating from idle to go, just slightly stumbling JUST PAST depression of the pedal.

    Jets, nozzles, accelerator pump, vacuum advance have all been changed earlier with the timing adjusted properly when out of the blue it starts this stumbling. No vacuum leaks. Unhooked the vac advance and plugged the carb tube - had no effect. Timing mark's right on the money (and hasn't been changed).

    Hot/cold, doesn't matter.

    It even stumbles at slow cruising speeds (below about 50mph) right after mashing the gas.

    Worked perfectly and started this without anything else being changed.

    What say you?

    lancer header8.jpg
     
    Last edited: May 1, 2018
  2. hoosierdaddy

    hoosierdaddy FABO Gold Member FABO Gold Member

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    accelerator pump ?
     
    • Agree Agree x 1
    • teringer

      teringer ase master hall of fame

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      check wiring on the pick up in dist for a rubbed thru spot and a bad plug wire.double check the gap at pick up coil
       
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      • Mattax

        Mattax Just the facts, ma'am FABO Gold Member

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        Old fuel leaves a varnish - if it sat
        Slowly accelerating is OK? If so, then go over the accelerator pump system. If it uses a rubber umbrella check valve, it may have become distorted by the latest fuel mix. IIf not, then a passage could be clogged, reclean circuits.
        Always Check fuel level in the bowls.
         
      • doc540

        doc540 Well-Known Member

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        removed the front bowl, cleaned everything with carb cleaner, nothing looked gunked up (full kit not too long ago)

        Seems to accelerate more consistently, but I'll have to drive it midday to get it up to full operating temp to test it.

        Thanks for all the suggestions.
         
      • AJ/FormS

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

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        Blow out the airbleeds, then
        Back to basics
        valve lash and compression test
         
      • jimjimjimmy

        jimjimjimmy lobsterman FABO Gold Member

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        it sure sounds like it is in the dist maybe the advance springs .
         
      • doc540

        doc540 Well-Known Member

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        drove it at full temp today - much improved

        thanks