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Thread: Lean siezure

  1. #1

    Join Date
    Dec 2005
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    Lean siezure

    I rode my ski today, yup the one i am trying to sell. On my way home it siezed. I let it cool for a while started it up and idled all the way home no problem. Pulled the head off and it had two small 1/16th of an inch square pits in the head and piston right by the exhaust port. Is that detonation? My wash is maybe a touch leaner than stock. I dont get it I am running 39.5cc domes with 100 octane sunoco. I am running 105,100,102.5 pilots and 135 mains. my lows are 1.5 turns out and my highs were 2.0 turns out. I dont get it???? I am stock porting. I have K&Ns and a head. what gives?


  2. #2
    jdog800's Avatar
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    What was your compression before and now? What piston was it....check rear seal you can look down between the motor and the coupler guard. If this seal blows it could cause your problem.

  3. #3

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    It was the front cylinder.

  4. #4
    jdog800's Avatar
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    also check pulse lines to the carbs. Check the fuel filter. Did you scar the cylinder

  5. #5

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    Fuel filter is new, as are all lines, pulse and fuel. I am not using the fuel valve anymore. I run off the reserve pickup only.

  6. #6

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    Oh and no scars at all. Everything looks fine, but if i run it again without changing anything it will let go. Is 39.5cc too much compression? I know with the 41cc i am at 155psi on my uncles ski with the same mods.

  7. #7
    jdog800's Avatar
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    there is no way other than a compression tester to know how much compression you have. You can buy one at your local automotive store. All motors are built slightly different, what gave you 155 in another ski may give you something very different. The only way to tell is a compression test. This will give you an idea of what octane gas you need to be running.

  8. #8
    jdog800's Avatar
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    do you still have the oil injection? And when you say your not useing the selector valve......did you bypass it do you have a open fitting that could suck air?

  9. #9

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    yes i still have oil injection. I have a line going from the reserve pickup to the carb and a return line. The ON pickup has a cap on it.

  10. #10
    cheatin' piston popper addicted's Avatar
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    what cdi?

    it could also be the front seals leaking

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