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OPS 90 tuning help needed

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Old 04-02-2008, 09:15 AM
  #1
fast9
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Default OPS 90 tuning help needed

I have a used OPS 90 that I had to put a new piston /sleeve into. I just started it for the first time and it starts right up but then wants to kick over and run backwards. Causes/ solutions for this? I have 30% fuel in it for now and a medium heat glow plug. If the timing in the motor has been changed I am not aware of it.
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Old 04-02-2008, 11:38 AM
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Default RE: OPS 90 tuning help needed

Are you using 12 or 24 volts to start it? If 12, consider switching to 24. On the big block engines, 12 volts aren't enough to overcome the compression, especially with a new piston/liner, and turn the engine at a good starting speed.
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Old 04-02-2008, 12:03 PM
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Default RE: OPS 90 tuning help needed

As above plus:

Is the backplate and disc back in the same place it came from?

Also, have you altered head shims at all to alter compression?

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Old 04-02-2008, 04:28 PM
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fast9
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Default RE: OPS 90 tuning help needed

I do have the 24 volt starter and it turns it well. It will start and run the proper direction for a few seconds and then stumble and reverse on its own. My disc opening begins to appear about 1/8" after the piston passes bottom dead center. I think this is correct? I reassembled using the head shims it came with(used). I am not sure about the thickness/number of the original head shims.
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