1971 Plymouth Duster with 3.7 225 Slant six Idles very rough

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  1. Donniedon

    Donniedon Member

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    I've had my '71 Duster engine rebuilt, as well as the Holley 1 bbl. carburetor. The mechanic I use suggested that I use Pertronix Distributor, and go pointless. It seems ever since, my idle has been very rough. Idles too fast, and really rough.
    1.) Electrically- - - completely new wiring harness throughout car, new alternator, spark plugs, coil, ignition wires.
    2. With regards to fuel intake- - - Rebuilt 1 bbl Holley Carburetor, new vacuum lines, hooked up properly, new fuel pump, new fuel filter, new gas tank ( total parts).
    3.) With regards to exhaust-- - new exhaust manifold, new single tailpipe, new muffler, and continued new tailpipe to rear bumper.
    I don't know what is going wrong. Any suggestions /advise would be welcome.
     
    Last edited: May 10, 2021
  2. rklein383

    rklein383 Well-Known Member

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    This is usually a process of elimination but since it has been upgraded to electronic. Make sure you have good ground from the engine to the frame. Since it is idling fast, that seems to indicate an air/vacuum leak somewhere.
     
  3. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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    Along with "the usual"

    Carb even though gone through may have a problem or not adjusted correctly, vacuum leak, timing bad plug or bad plug wire, bad valves or if valves adjustable, not set correctly, and on we go

    BUT ONE possiblility is that somehow the Pertronix is AFU or installed wrong and you are suffereing from what is called (bad) "rotor phasing"

    Google it several articles and videos on the www. This means that due to some problem in the distributor, the pickup device is not firing the spark when the rotor is actually pointing at a plug wire distributor cap contact

    Ignition Systems - Rotor Phasing Article by MSD Ignition | Hotrod Hotline



     
  4. Slantsix64

    Slantsix64 Well-Known Member

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    Always always on a slant six adjust the valves first. Tight valves will give a rough fast idle.
     
    • Agree Agree x 1
    • Donniedon

      Donniedon Member

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      Thanks! I will look into ALL of the items suggested!
       
    • ESP47

      ESP47 Well-Known Member

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      I vote vacuum leak. Most likely at the intake to head connection.

      The valves are probably too tight as well. slantsix.org has a write up on how to do the adjustment correctly.
       
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