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Thread: Sl780 acting up

  1. #1

    Sl780 acting up

    Howdy! I have an issue with a 1997 Polaris sl780 in a 12' Jon boat, I tore the motor down due to overheating (coolant line broke, smoked middle piston) but I have been battling a condition where the ski bogs and the rear piston is clean. Ski bogs at low rpms. I swapped plug wires, changed head gasket, resealed exhaust etc. I got this used and the last owner did a shoddy rebuild as the ski had a hole in the piston when he got it, there were pound marks in one of the heads and he slapped that back on so I'm not against doubting his work. I am getting spark on all cylinders, went through the carbs (mikuni kits, pop-off tested, resealed reeds etc. This is baffling me, hoping someone has had the problem before and can help me.

  2. #2
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
    Join Date
    Oct 2006
    Cleveland OH
    Welcome to the Hulk

    If the PTO piston dome is clean, you have water intrusion or an overly rich condition, or no spark on that cylinder.

    If completely clean, you most likely have water intrusion.

    Since you overheated, did you check your head and cylinder for warpage?

    You stated you have spark, have you verified it while running with a spark tester installed?

    Reeds sucking air won't cause an overly rich condition. A broken reed will though.

    When the engine is running, remove the flame arrestor and see if that cyl is spitting more fuel out the top than the other 2. If so, bad or broken reed.

    Are your carbs in sync? Meaning throttle plates open the exact same time and amount? They can be adjusted.

    Did you verify the jets were the correct size in the carbs?

    Previous owners do stupid things and you need to assume everything is wrong. (not kidding)

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