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  1. #1

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    Polaris sl 750 need help

    New to the forum have learned a lot from here. Thanks to all that help. I just picked up a 94 Polaris with a burnt hole in the front piston. I understand that several things could have caused this. Carb running it lean maybe no water flow and so on. But when I pulled the jug there was 3" of oil in the crankcase. Ive been around 2 cycles but never ski motors. Im pretty sure theres not suppose to be any oil in the crankcase right? Im guessing these oil injections do not mix with the fuel like outboards? My plans are to just replace the one piston clean carbs and mix my own fuel to see if I can get this thing running. I don't think blocking the oil injection will hurt anything will it? Thanks


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    Welcome

    Generally speaking the Polaris oil injection system is reliable when properly maintained. Failures are often traceable to old oil hoses or loose clamps, perhaps a clogged oil filter or even forgetting to put oil in the oil tank.

    The liquid oil in the engine may have been someone's attempt to "protect' the engine until it could be prepared.

    The oil nipples on the engine may have internal check valves to prevent oil drooling into the engine when the engine is not running. Sometimes the check valve gets stuck open and oil slowly drains from the oil tank into the engine.

    Since carburetor cleaning and full rebuild is needed to ensure the replacement piston does not burn down, be sure to clean and check the oil feed at the same time. Do all three carburetors, of course.

    See my signature links for other common maintenance items and recommended upgrades. One such upgrade is the triple outlet fuel pump.

  3. #3

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    Thanks K for the advise. I will go ahead and probably replace the oil lines and check the check valves. This is my first ski. My plan was to just patch the motor back togather and if it all works out and we enjoy it I was going to do a full rebuild over the winter.

  4. #4
    BlueFishCrisis's Avatar
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    Patching the motor together and running it may lead right back to where it is now, with a burnt piston. Need to find out why it put a hole in the piston first. Fuel system upgrades are a must do, including upgrade to the triple outlet pump, replacing the fuel lines and filters, and making sure the fuel shut off is in good working order and not leaking air. Be sure the return restrictor is in place and you need to open up the carbs to be sure nothing is corroded or stuck.... Ideally, do all of this, and fully rebuild the carbs, and you will likely NOT have an issue....

  5. #5

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    Thanks blue fish. I am going to do everything you stated. Two of The cylinders still have 120lbs and look good. The mag cyclinder is the bad one. Just dont have money right now to rebuild the whole motor. I bought a piston and was going to hone the one cylinder. I also marked on the crank best I could 120 degree marks. Turned the crank and there was a piston tdc at each mark. And what is the return restrictor?

  6. #6
    BlueFishCrisis's Avatar
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    From the factory there was a small brass fitting installed inside the return fuel line, usually identified with a zip tie 1-2" after the carbs. If someone previously replaced the fuel lines and didn't know about the restrictor, it may be missing. It helps keep the system fuel pressure up instead of the fuel simply returning to the tank.....

  7. #7

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    Got it thanks man. Hopefully I'll get it back togather at the end of next week and let ya know how it goes.

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