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Thread: PRM jump

  1. #1

    PRM jump

    I have a 780 SL and It can't get it to go between 3000 and 4000 RPM. Once I try and get above 3000, it jumps to 4000RPM and when I drop below 4000, it falls down to 3000. This is very frustrating as that is the speed I want to pull skiiers. Any help would be appreciated!


  2. #2
    I'D RATHER SWEAT THAN SHIVER hyoctane23's Avatar
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    Thats what happens when you "get on the pipe." In other words, that is when the exhaust wave pulses align with the design of the expansion chamber on your ski. Nothing you can do about it. What top RPM are you getting?

  3. #3
    Quote Originally Posted by hyoctane23 View Post
    Thats what happens when you "get on the pipe." In other words, that is when the exhaust wave pulses align with the design of the expansion chamber on your ski. Nothing you can do about it. What top RPM are you getting?
    It tops out at 45MPH and 6000RPM. Is this a design flaw? I have been on many Polaris jet skis that don't do this.

  4. #4
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Welcome to the Hulk.

    Something isn't right with your ski.

    It should turn 6500 RPM max and be able to turn 3800 RPM without getting on the pipe.

    Your max speed should be in the low 50 MPH range.

    Check your carb settings

    Check your impeller

    and check your compression.

  5. #5
    I'D RATHER SWEAT THAN SHIVER hyoctane23's Avatar
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    Hmmm...what else could it be then? Probably isn't cavitation because that would happen on take off more than likely. I just remember my SL780 always hitting the pipe around 4k RPM??

  6. #6
    Click avatar for tech links/info, donation request K447's Avatar
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    I don't think this has anything to do with exhaust pipe resonance.

    Might be something in one or more carbs is clogged or out of whack.

    Some of these CDI have a significant change in ignition timing around the mid-range RPM, and that can create a sudden change in engine power as the CDI adjusts the timing advance at the RPM threshold.

  7. #7
    I'D RATHER SWEAT THAN SHIVER hyoctane23's Avatar
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    Touché. I'm still curious though how a fuel problem would cause a sudden increase in power? I could see how the CDI could do that with a sudden advance in timing.

  8. #8
    Quote Originally Posted by hyoctane23 View Post
    Touché. I'm still curious though how a fuel problem would cause a sudden increase in power? I could see how the CDI could do that with a sudden advance in timing.
    Is the anything that you can adjust on the CDI? What should I search on to tune this up?

  9. #9
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Quote Originally Posted by hyoctane23 View Post
    Hmmm...what else could it be then? Probably isn't cavitation because that would happen on take off more than likely. I just remember my SL780 always hitting the pipe around 4k RPM??
    Correct, right around 4k RPM is when it takes off. So 3800 is right about the cut off before she really starts to pull.

  10. #10
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Quote Originally Posted by K447 View Post
    I don't think this has anything to do with exhaust pipe resonance.

    Might be something in one or more carbs is clogged or out of whack.

    Some of these CDI have a significant change in ignition timing around the mid-range RPM, and that can create a sudden change in engine power as the CDI adjusts the timing advance at the RPM threshold.
    I'll agree, maybe his carbs are out of sync. or adjustement.

    The timing is at full advance at 3000 RPM, so I think he's feeling when the pipe or carb issue comes into play. I don't think it's the CDI.

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