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  1. #1
    Lucian
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    97 polaris 780 will not rev over 5600rpm

    will not rev over 5600 rpm @ 36mph. has about 55 hrs. 120 psi on each cylinder. cleaned carbs, fuel pump, and fuel filter. drained old gas out. retightened all fuel lines. new plugs. got plugs to burn golden with stock carb adjustments with minor twicking.

    it will run good to 5600rpm. after it reaches 5600 it will then want to cut up and slowly lose power. not sure if it is a lack of gas or a to much gas. if i let off throttle at 5600 while it is cutting up it will not accelrate good again, unless i cut off the gas for a second until power returns (then turn gas back on.) it will then reach about 5600 and then begin to cut up again. if i stop and idle then it will jump out of the whole with good power until 5600 until it cuts up again. i noticed a air pocket on the roof of the fuel filter.?. i have read the forums a few times. studied the manual. it is bone stock to my knowledge.


  2. #2
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Welcome to the Hulk Lucian.

    Something else is going on with your ski, 36 MPH at 5600 RPM is extremely low. Should be closer to 46 MPH at that RPM.

    Start with checking the jet pump for broken fins and/or bad bearings. Also look for excessive wear between the impeller and wear ring.

  3. #3
    Lucian
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    the impeller was stuck when i bought the ski. the motor wouldnot turn over, but after i took off the impeller and associated parts, ( i guess it would all be called the jet drive?) the motor fired right up. after i inspected it further, the housing for the impeller had a high spot that caused the impelled to not turn. i simply filed down the high spot until it rotated freely. the impeller itself could have damage that my eyes do not see. i can say that the blades themself have nicks on the edge, but nothing severe that i can see. although the pitch could be off. is there anyway to check it beyound visual inspection?

    stock carb setting...lower were 1 3/8 out from seated.. the upper front 1 1/8, center 7/8 and rear 1 1/4. why are the uppers all different. i got this from the alt 785 manual via the HULK.

  4. #4
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    The impeller stuck could be a bad thing. The crank shaft is only a press fit design, so if it stopped abruptly, it may have thrown the crank out of index. You need to index the crank before you go any further.

    You need to "search" for crank index on here. Use a degree wheel and a dial indicator to verify the piston TDC is exactly 120* apart. If they aren't, you'll never get the performance and/or may damage pistons regularly.

    The Carb screws are different because each cylinder has different fuel requirements. For example, the MAG (front) runs hotter than the others. Hotter temps require more fuel to prevent detonation.

    Axs for the carb settings, the PRO 785 settings will not work on your ski. You need to follow the settings for your specific ski.

  5. #5
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by Lucian View Post
    the impeller was stuck when i bought the ski. the motor would not turn over, but after i took off the impeller and associated parts, ( i guess it would all be called the jet drive?) the motor fired right up. Jet Pump is the name.
    after i inspected it further, the housing for the impeller had a high spot that caused the impelled to not turn.
    That would be called the wear ring, around the impeller.

    i simply filed down the high spot until it rotated freely. the impeller itself could have damage that my eyes do not see. i can say that the blades themselves have nicks on the edge, but nothing severe that i can see.
    although the pitch could be off. is there anyway to check it beyond visual inspection?
    Welcome to the Hulk!

    You have downloaded the 1992-1998 Service Manual - correct?

    There is information in there regarding checking the clearances between the impeller to the wear ring around it.

    Could you explain how there could be a bump on the inside of the wear ring big enough for the impeller to get jammed? Photos perhaps?
    Was the pump dropped while off the hull?

    Checking the pitch on your impeller accurately can be tricky. You either need a special pitch gauge, or send it to one of the places that repairs, rebuilds, and often can modify the impeller. Several guys on here have the skills.

    Check for excessive wear ring clearance, then go from there.
    Last edited by K447; 06-03-2008 at 02:27 PM.

  6. #6
    Lucian
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    i bought the ski from a fella that bought the ski from a fella. dont know any of the history expect it is out of texas. how the impeller got stuck, i dont know. i am sure the grinding did not help the wear ring. i will check the 120 rotation per piston. i think it is a fuel problem personally, but yet to find a rebuild kit for the fuel pump. also the link to the service manuals opens, but will not let me download the proper manual. it acts like it is loading, but nothing come up in the end. i set my carbs based on the slt785 pro. could be my entire problem. will keep you posted. thanks for the insight peoples. i appreciate your knowledge and thoughts.

  7. #7
    Moderator beerdart's Avatar
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    Quote Originally Posted by Lucian View Post
    i bought the ski from a fella that bought the ski from a fella. dont know any of the history expect it is out of texas. how the impeller got stuck, i dont know. i am sure the grinding did not help the wear ring. i will check the 120 rotation per piston. i think it is a fuel problem personally, but yet to find a rebuild kit for the fuel pump. also the link to the service manuals opens, but will not let me download the proper manual. it acts like it is loading, but nothing come up in the end. i set my carbs based on the slt785 pro. could be my entire problem. Where did you find those specs? Polaris never made a SLT 785.will keep you posted. thanks for the insight peoples. i appreciate your knowledge and thoughts.
    The manual is large (36meg)and will take some time to download.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  8. #8
    Lucian
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    set the carbs via correct setting. it responded great. it 6500 rpm with out hesitation. (althought top speed was only 42mph, i am sure the impeller is the cause) the motor however was running like i think it should. until it started to act up again. would not rev over 4900rpm and cut up while it was reaching the 4900 mark. i ran it around playing the carbs again, along with the plugs. then cleared out again, but shortly after went back to the 4900. i would suspect trash in a jet ot two, but since i am going in to the carbs a 3rd time. i was wondering where to find a rebuild kit. (thinking possible float issue, as it has been sitting for a few years.) Not sure where to look for the rebuild kit. yet to find a local PWC dealer. thanks again to those who take the time to help a newby out. @-----

  9. #9
    Lucian
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    it was a carb needle seat. it is running great. although it hits the rev limiter off the line as i think the impeller being damaged is making it lose thrust threw he entire rpm range. its top speed is only about 44mph at 6500 rpm. working on finding a better jet drive.MLD

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