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  1. #1

    Can't figure this out -


    Can anyone tell me why my 97 polaris SLT 780 suddenly rockets from 38 mph at full throttle to top speed (55/58 mph) and full rpm after hitting a few well timed waves or a hard right turn. This seems to be the only way to achieve top performance / speed. Once I get it to top rpm / speed I can keep it there indefinitely. However, 40 mph is as fast as I can get it to go once I back off the throttle until I hit a few good waves again or a hard right turn. This type of behavior doesn't seem to be remedied or consistent with simple carb adjustments (but maybe I'm wrong). I did a cold compression check (all in the low 120's) . This ski runs smooth low to midrange and idles well. Might not pull out of the water as fast as I'd like it to, but maybe that is also part and partial to its "top speed challenge". I'm not sure as I'm new to this ski. I have noticed thatthe fuel/water separator drops to half full when running mid throttle. (is this normal?) Also, this ski seems to use a lot of fuel. Any suggestions are really appreciated.

    Having said all that, this is what I have done so far to try to remedy the problem:
    • Rebuilt carbs to spec (including checking pop off),
    • Installed new fuel lines
    • Ran a compression check - is good on all three cylinders -120’s cold
    • Rebuilt fuel pump
    • Checked ventilation check valves,
    • New plug wires.

      So now, I’m thinking it might be a sending unit problem but repair manual says thatthere is no sort of "turn over check valve" inside the fuel tank asin older models. But does anyone have experience with fuel uptake/ sending unitproblems as it might relate to fuel delivery? Is there a possibility of ahairline crack in the sending unit? Hate the thought of having to remove thefuel tank out...looks like a pain in the butt. Additional info...my MultiFunction Display is disconnected...but I doubt that would have anything to withnot being able to achieve top end speed at WOT (such as rev limiterinterfering) I can achieve top end revsafter a hard right turn. It was mentioned that the stator might be theculprit…but that doesn’t seem consistent with its behavior either. I have ran this question on another thread but wanted to fresh the update after some time to implement some suggestions but any new suggestions are greatly appreciated.


  2. #2
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    Does it slow down when you turn hard left? It could be a fuel delivery issue. Did you check the fuel shut off valve? Are all of your fuel lines connected to the right place on the sender? Check your pulse line for kinks or sharp bends.

  3. #3
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    Check for fluids in the pulse lines too.

  4. #4
    Quote Originally Posted by BryanP View Post
    Does it slow down when you turn hard left? It could be a fuel delivery issue. Did you check the fuel shut off valve? Are all of your fuel lines connected to the right place on the sender? Check your pulse line for kinks or sharp bends.
    Thanks...I'll try that

  5. #5
    Quote Originally Posted by fixer View Post
    Check for fluids in the pulse lines too.
    Thank's ...I'll do that also...Thanks a bunch

  6. #6
    Quote Originally Posted by fixer View Post
    Check for fluids in the pulse lines too.
    Is this a bad thing?...fluid on the back plate of Mikuni fuel pump


  7. #7
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    Quote Originally Posted by polaris780slt View Post
    Is this a bad thing?...fluid on the back plate of Mikuni fuel pump

    Check the lines too, they probly have some trapped at the bottom.

  8. #8
    Quote Originally Posted by fixer View Post
    Check the lines too, they probly have some trapped at the bottom.
    So I assume fluid behind the diaphram is not desirable? I'll check the lines too. Thanks for the help

  9. #9
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    I believe the one side of the diaphragm the comes from the pulse line should be dry

  10. #10
    Quote Originally Posted by BryanP View Post
    I believe the one side of the diaphragm the comes from the pulse line should be dry
    Click image for larger version. 

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    This the back side and opposite of the pulse. There is no way for fluid to get behind the clear see through diaphram. So I'm thinking micro perferation or it was left there on purpose during a previous rebuild. I'm also thinking it shouldnt be there...am I correct?


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