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  1. #1

    1995 polaris 750 sl burning hole in piston

    Hello, I am looking for some help on a project ski my dad and I are finishing. It is a 95 polaris 750 sl. It keeps burning a hole in the piston nearest the bow. I have been hearing that upgrading to a mikuni 3 outlet fuel pump is the common solution. But, I just want to be sure before I putting parts on it for no reason. Also, on the blue Fuji engines, are the timing marks in the little black cap on top of the stator? Thanks


  2. #2
    thester71's Avatar
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    Quote Originally Posted by illusionman101 View Post
    Hello, I am looking for some help on a project ski my dad and I are finishing. It is a 95 polaris 750 sl. It keeps burning a hole in the piston nearest the bow. I have been hearing that upgrading to a mikuni 3 outlet fuel pump is the common solution. But, I just want to be sure before I putting parts on it for no reason. Also, on the blue Fuji engines, are the timing marks in the little black cap on top of the stator? Thanks

    The tripple outlet pump should eliminate the problem, Make sure the rest of the fuel system is in good shape, the grey tempo fuel lines also cause problems as well as dirty carbs. How many pistons have you holed? That piston dust is very bad for the crank bearings.

  3. #3
    Click avatar for tech links/info, donation request K447's Avatar
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    JUST replacing the fuel pump with a triple outlet version is not enough.

    The carbs must be opened up, cleaned, checked, and rebuilt. Use a genuine Mikuni rebuild kit.

    Set the carb screw adjustments to specification.

    All fuel lines should be replaced, including any inside the fuel tank. Same with the oil lines. New oil and fuel filters too.

    If there is a restrictor slug inside the return fuel line, make sure it gets transferred to the replacement fuel line. If it gets missed, you will not have proper fuel pressure.

    The fuel selector valve should be taken apart and cleaned up, possibly with a new and lightly greased O-ring.

    Make sure the inside of the fuel tank is clean. No dirt, no water.

    Get the fuel system 100% good. That will keep your pistons happy

    Another possible cause is an air leak in that cylinder. Often air leaks happen around the crank shaft seal, or leaking gaskets in the intake manifold/reeds/carbs.

  4. #4
    thanks for all the help guys, I really appreciate it. I think there has only been 2 pistons blow. I got the ski from my step dad who replaced it twice, so lets hope it doesn't blow another!

  5. #5
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by illusionman101 View Post
    ...there has only been 2 pistons blow.

    I got the ski from my step dad who replaced it twice, so lets hope it doesn't blow another!
    You really need to make sure the cause of the piston failures is corrected, not just the resulting piston damage.

  6. #6
    Connecticut CrazyA's Avatar
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    Quote Originally Posted by illusionman101 View Post
    thanks for all the help guys, I really appreciate it. I think there has only been 2 pistons blow. I got the ski from my step dad who replaced it twice, so lets hope it doesn't blow another!

    Pictures please....

  7. #7

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    If you putting a hole in the piston nearest to the bow (front cylinder) ignition timing is out the ignition is fixed of the front cylinder So crank index should be out. I have had this happen with Air leaks (like crank seals or even bad case sealer must use threebond 1211), lean carbs that can be blockage in the carbs causing a lean condition.
    Once we see some pics it will a bit easier to say.
    The carbs on these 650,750, 780 are a little bit of a problem but once you get them dialed in there good.

    Install that new fuel pump run the 3 separate fuel lines to each carb blocking off the extra lines that connect the 3 carbs together run the pulse line right to the case rear cylinder pulse line and block off any other if any them all 3 return lines will run into 1 and back to the tank.
    Have you done anything with the thermostat? If so what?

    There was a problem with CDI's years ago that sometimes 1or2 out of 100 or so caused some advancing I had 3 over the years that I had to replace because of this problem.
    But 99% of the time it was Crank index, air leak or lean carbs in some way.
    I see that your new to hulk but I’m sure with all the Polaris guys here we can help.
    Good Luck post some PICS

    Doug

  8. #8
    kraven's Avatar
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    Cool

    Quote Originally Posted by illusionman101 View Post
    thanks for all the help guys, I really appreciate it. I think there has only been 2 pistons blow. I got the ski from my step dad who replaced it twice, so lets hope it doesn't blow another!

    I had a a pair of POLARIS 94 SL750's, went through 2 pistons in the one ski, ended up the crank was out of index, and this is when the ski was new and under warranty back in '94

    The other one ran great, never a problem

    The dealer had/made this 2 -piece collar and degree wheel, that clamped over the P.T.O. end, was able to diagnose it without engine removal.


    Hope this helps

  9. #9

    95 Polaris sl750 that just won't start after hitting a "bump"

    Hello,

    I recently purchased a '95 SL750. It was lightly used but has sat for a bit with winterizer in the carbs/fuel lines. I got it started and rode it for a very short time mostly at idle. It was rough. Replaced the plugs.(one was smashed) Back in the water.. it fired right up. Idled over to a floating lift and parked in for 10 minutes. Now, it will not turn over! Don't think it's getting fuel. I'm seeing spark. Doesn't even try to start other than when I let it sit overnight. Tried but failed and back to no ignition whatsoever. Could the "bump" up on to the lift have caused an issue? Any diagnosis help would be greatly appreciated. Thanks!

  10. #10
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by Papajohn2 View Post
    Hello,

    I recently purchased a '95 SL750. It was lightly used but has sat for a bit with winterizer in the carbs/fuel lines. I got it started and rode it for a very short time mostly at idle. It was rough.

    Replaced the plugs.(one was smashed) Back in the water.. it fired right up.

    Idled over to a floating lift and parked in for 10 minutes. Now, it will not turn over!

    Don't think it's getting fuel. I'm seeing spark. Doesn't even try to start other than when I let it sit overnight.

    Tried but failed and back to no ignition whatsoever. Could the "bump" up on to the lift have caused an issue? Any diagnosis help would be greatly appreciated. Thanks!
    Welcome to the Hulk

    What do mean by the spark plug being 'smashed'?

    Are you talking about the electrode end that sicks into the cylinder?

    What spark plugs were installed?
    What spark plugs are installed now?

    How strong is the spark you are seeing?
    Blue-white, or yellow spark?

    Have you checked cylinder compression?
    Note: All spark plugs out, throttle held wide open.

    What is the battery voltage when cranking?

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