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1990 Force 90 hp timing (Prestolite ignition) Bench test

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  • 1990 Force 90 hp timing (Prestolite ignition) Bench test

    I did a static timing (cranking-speed 970 RPM) the timing is out way past 28 degrees (more like at TDC but at WOT (static) it is bang on??
    working on 1990 force 90 horsepower Engine serial. 17523 Engine model. 906X90B

  • #2
    Sounds like the throttle wasn't advanced all the way when doing the test?
    Or the plugs weren't removed?


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    • #3
      Hey Guys,

      I forgot to mention; The key is not sheared & TDC is bang on.
      All plugs are out and the Throttle is held open with a bungee-cord.

      When I bought this motor, the previous had "played" with all the possible adjustments from Carbs. to the timing, so I want to start fresh.

      at what position should the Tower-shaft & Idle-screw be? when checking the timing at Cranking with Throttle off
      (Carbs closed)

      I have the Brunswick Force Service manual, but I seemed to not fully grasp this step
      working on 1990 force 90 horsepower Engine serial. 17523 Engine model. 906X90B

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      • #4
        You set the timing static or dynamic with the throttle at WOT.
        No timing set at idle.
        The timing at idle will be what it will be, depending on the idle speed.
        Idle as low as possible will end up with a timing about 3-5 dgr BTDC.

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        • #5
          Thank you Nordin,
          That explains my question also on how you could adjust it twice?? ,meaning if you adjust it at Cranking-speed (throttle closed & at changing it at cranking-speed WOT

          I'll verify my adjustments tonight & re-read the chapter
          working on 1990 force 90 horsepower Engine serial. 17523 Engine model. 906X90B

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          • #6
            Hi Nordin,

            just dwelling on the steps with the timing;

            I adjust the timing (static) at cranking speed WOT at 28 degrees and what ever the timing is at throttle is closed will be close to TDC as you said; 3-5 degrees before TDC
            working on 1990 force 90 horsepower Engine serial. 17523 Engine model. 906X90B

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            • #7
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              Okey then you have set the timing right.
              Dynamic will give you about 30-31dgr at WOT if you set it 28dgr static.

              Dynamic is the best BUT you will need an assistant.
              BTW you will not notice any big differnt in performance if the timing is 32dgr or 30dgr.

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