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  1. #1

    high compression

    Hi guys, have a polaris 750 that has a mag compression of 175. Center is 170 pto is 168.. I just replaced the mag piston, due too hole. Bought it cheap. Also changed out the plugs from 7's to 8. Im concerned about the high compression. Other ski compression is 135 all three. Ran good for a min before burning hole in piston. Any advice would be helpful. All piston are .5 over


  2. #2
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    If your compression is that high you are going to need some serious octane in your fuel

  3. #3
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by cg560 View Post
    Hi guys, have a polaris 750 that has a mag compression of 175. Center is 170 pto is 168.. I just replaced the mag piston, due too hole. Bought it cheap. Also changed out the plugs from 7's to 8. Im concerned about the high compression. Other ski compression is 135 all three. Ran good for a min before burning hole in piston. Any advice would be helpful. All piston are .5 over
    Welcome

    Are you confident your compression gauge is reasonably accurate?

    Does this engine look stock or has aftermarket parts?

  4. #4
    Also im wondering about carbs. They are from a 780. Rebuilt them but not sure were too set the high and low adjust.

  5. #5
    It looks stock. Im confident im getting correct readings. Other skis are all on point.

  6. #6
    BlueFishCrisis's Avatar
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    The standard 750 is 120 psi after a fresh rebuild. Take a close look at the motor. There should be a base gasket between the cylinder and crankcase. There should also be a head gasket. Eliminating these and using gasket maker can replace the gaskets, but will raise the compression.

    Post some photos so we can see what you have.....

  7. #7
    all the gaskets are there, I bought replacements. This machine is all souped up with performance parts, wondering now if heads were milled. going to try double head gaskets and see if it lowers compression a bit.
    Im still stuck on carb issue. been rebuilt but not sure were to set needles. (780 carb on a 750)

  8. #8
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    You can run it with the high compression, you just need the proper octane fuel to support it.

  9. #9
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    Quote Originally Posted by BryanP View Post
    You can run it with the high compression, you just need the proper octane fuel to support it.
    Sometimes the timing should be retarted a bit as well.175 psi is very high.

  10. #10
    Can't tell you where to set the carb adjustments bcause I'm not a pro at this yet but I've been dinking with my 97 slt 780 and all the carbs are set the same and the 96 780 carbs have different settings. Can find the info in the manuals. You might know this already but if not I thought I would just throw it out there to help.

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