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  1. #1

    Join Date
    Jun 2010
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    94 sl750 hole in piston again!!!!

    bought ski with hole in #1 piston, other pistons looked new so replaced it, ran great for 10 min. then blew hole in #3. whats weird is that the spark plug that was in the #1 cyl. looked like it was getting really hot. so after replacing piston i put it in #3 just to see if it was the plug? and behold it blew #3 piston.could it just be a coincidents or to hot of plugs or??? im using autolite 63's


  2. #2

    Join Date
    Sep 2009
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    St. Louis, MO
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    220
    sounds like it. stock is bpr7es i believe you can run the 8's without a problem too. that's what I run in my 650 & 780.

    Why are you running autolite's though instead of stock?

  3. #3

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    Jun 2010
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    sutter, ca.
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    the plugs were in the ski when i bought it, i also cut the oil line and pluged it off and ran pre-mix. is it a good idea to just plug the line going into the oil pump? could it suck air somehow?

  4. #4
    blegan's Avatar
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    May 2008
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    bakersfield
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    321
    Quote Originally Posted by 3-banger View Post
    the plugs were in the ski when i bought it, i also cut the oil line and pluged it off and ran pre-mix. is it a good idea to just plug the line going into the oil pump? could it suck air somehow?
    When going pre-mix you must at very least pull the gear & shaft, both are lubricated through the oil being pumped & you are now not pumping oil through it! As for the pistons burning holes thats probably a lean fuel cond. # 1 & #3 are known to hole due to 1 of 3 things crank out of index,main seals,lean fuel cond..I would really check where you pulled the oil lines & be sure to go through fuel sys. while you have it apart.
    Good Luck Brian

  5. #5

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    Jun 2010
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    sutter, ca.
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    thanks for the help ,i'll probly hook the oil line back up to be safe and not run pre-mix.

  6. #6
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Oct 2006
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    Cleveland OH
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    Here's some causes of a holed piston.

    http://www.greenhulk.net/forums/show...urndown-Basics

    Just replacing the piston and not fixing the problem that caused it WILL result in another damaged piston.

  7. #7

    Join Date
    Jun 2010
    Location
    sutter, ca.
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    16
    yes i have messed w/carb adj. can anyone tell me what to set the low and high screws to start out with? i have no manual. this mite sound dumb but which one is the low & high? and why is this a common prob. on these skis? was there ever a recall? thanks...

  8. #8
    blegan's Avatar
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    Quote Originally Posted by 3-banger View Post
    yes i have messed w/carb adj. can anyone tell me what to set the low and high screws to start out with? i have no manual. this mite sound dumb but which one is the low & high? and why is this a common prob. on these skis? was there ever a recall? thanks...
    mag 1-1/4 center 3/8 pto 7/8 Those are for high speed & low speed is 1/2 turn for all 3 Its just like it says high speed is highest on the carb body & the low is the lower

  9. #9

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    Jun 2010
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    sutter, ca.
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    thanks, I think i might of found the prob. I set all the high's @ 3/4 of a turn. could this be why I burned the piston?

  10. #10
    johnsonmtz's Avatar
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    Oct 2006
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    Mt. Zion Illinois
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    Quote Originally Posted by 3-banger View Post
    yes i have messed w/carb adj. can anyone tell me what to set the low and high screws to start out with? i have no manual. this mite sound dumb but which one is the low & high? and why is this a common prob. on these skis? was there ever a recall? thanks...
    Okay, you're throwing money at this ski without getting at the root problem. Holed pistons are the result of a lean condition. The 750's can be very reliable, but due to OEM design flaws in the fuel system, and problems with age and alcohol based fuels, they will burn pistons unless the appropriate upgrades and maintenance are done.

    You need to read the page created by K447 to get a full understanding of the known problems for your 750: http://polarispwcknowledge.shorturl.com/

    Basically there are several problems these machines can have. The usual list of updates/maintenance that MUST be done are:

    1) Completely tear down the carbs, thoroughly clean all passages with solvent, install new needles and seats, and reassemble with genuine Mikuni rebuild kits.
    2) Upgrade to a 3-outlet fuel pump
    3) Ditch the Autocock.
    4) Replace all OEM fuel lines with alcohol resistant 1/4" tubing. This includes the pickup lines in the tank.
    5) Clean out the fuel selector switch


    Carb Settings are as follows:
    Low Speed Needles = 1/2 turn out from seated
    High Speed Needles=
    MAG - 1/4 turn out from seated
    CEN - 3/8 turn out from seated
    PTO - 7/8turn out from seated

    Pop-off pressure should be between 10PSI and 18PSI.

    KJ

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