more big block duster tuning

Discussion in 'General Motoring' started by sackattack84, Jul 21, 2006.

  1. sackattack84

    sackattack84 Guest

    Posting yet again about the same car ('75 plymouth duster w/ 400 big
    block, 727 auto, 8.75" rearend, Holley 4160 600cfm vacuum secondary carb,
    mild cam of unknown specs). Just about have the engine sorted out now,
    with the exception of a hesitation when I punch the gas. The car does not
    hesitate under light throttle application and also does not hesitate if I
    give it a little gas and then stomp on it. It only happens when I give it
    moderate to heavy throttle from idle. I want to suspect the carb, but I am
    still learning and don't have a whole lot of tuning experience yet, so any
    suggestions would be helpful. Could a rich/lean condition of the
    accelerator pump be causing this condition? Thanks for the advice!
    sackattack84, Jul 21, 2006
  2. sackattack84

    OldSchool Guest

    sackattack84 wrote:

    You don't say, but I suspect you've got 3.55 or 3.92 rear gear and std
    torque converter. Might be that the secondaries are opening too early.
    See pg 12 of the Holley 4160 ref. here for more info:

    Also, Holley has a tech support line and on-line help, as noted below:

    "Online Tech Help, If you have questions about our products, need a
    part recommendation, or just cant seem to find what you need you can
    contact our Tech Support online and receive answers by e-mail.

    Holley Performance Products provides award-winning technical support
    via phone Monday through Friday, 8AM to 5PM CST @ 270 781-9741."

    See their web site for more
    OldSchool, Jul 21, 2006
  3. sackattack84

    John Kunkel Guest

    With the engine off, look down the primaries on the carb while briskly
    opening the throttle and observe the pump shot.
    A weak pump shot can cause the hesitation you are experiencing.
    John Kunkel, Jul 21, 2006
  4. sackattack84

    sqdancerLynn Guest

    How does it idle?? How much vacuum at Idle? If you have a big cam I would
    bet the throdle blades are too far open causing the hesitate. Sometimes
    requires very small holes to be drilled in the throdle blades to let the
    enging get more air without the throdle blades open past the transisiton
    point. Had to do that to my 750 holly on a 360hp/360 motor.Turn the carb
    upside down & look into the pri side their should be a slot in the body,
    the throdle blade should be in the middle of it. A good distributor is
    also a must. Just as a starting point run 10-12 degrees of inital
    advance, 22 in the dist depending on compression & type of gas something
    around 36 deg total with vacuum disconnected & plugged. You may find that
    600 a little small for a HP 400. I used the 750 Holly & sometime the 850
    sqdancerLynn, Jul 22, 2006
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