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  1. #1

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    Oct 2012
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    1999 gp800 high rpm, low rpm,

    Hello everyone, two weeks ago my son bought a 1999 gp800, with 100 hrs on it, from a retired couple. I could tell that the ski hasnt been the water all summer.
    The first time we took it out it ran like a scalded dog. With my boat GPS, i clocked it at 63 mph. I was very impressed.
    The second time we took it out the ski ran great for hour then all of the sudden, while riding it, the motor dies. The ski started right back up. But then it would not run past 7000 to 7500 rpm. While we headed back to the dock it died again but started back up.
    When we got home i hooked the water to it and started it up. Almost immedictely it revved to 5000 rpm and would not shut off. I pulled the lanyard, pressed the kill button, took both plug wires off, and then i disconnected the fuel line, whitch then it finally shut down. All this happened in under 30 seconds. I was scrammbling. I check the compression its good at 150 /160. Also no sighns of pitting on top of the pistions. But as you can see in the picture, of the spark plugs, one cylinder is running lean.
    Heres a little history about myself.I got my first ski at 10 yr, kawi 440, raced Mx for 8yrs. I have had a few sea-doos, and to date my sone races KX-250. On the ski we mix the gas with maxima castor 970 at 45 / 1. The automatic oiler is blocked off. Very sorry for the long post. Someone please give me some wisdon
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  2. #2
    crashhard's Avatar
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    Pull the carbs off and rebuild them. Thats where you want to start and probably all it needs, its not a big job just take your time.

  3. #3
    Quote Originally Posted by crashhard View Post
    Pull the carbs off and rebuild them. Thats where you want to start and probably all it needs, its not a big job just take your time.
    That wouldn't cause it to do a lean runaway, would it? I'm thinking he has an air leak, perhaps on the shaft seals?

  4. #4
    Yamaha artisan Cutlass's Avatar
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    Yah, I would consider running a pressure test on the motor. Sounds like you potentially have a lean runaway. Empty carbs can cause a lean runaway but I wouldn't think that was the issue, since you've been riding it.
    Read this thread:
    http://www.greenhulk.net/forums/showthread.php?t=9408

  5. #5

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    Thank yall. I will give this a try and keep yall posted

  6. #6

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    Oct 2012
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    now when you pressure test the motor where do you hook the kit up too?

  7. #7
    silvercrxsir's Avatar
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    The compression seems rather high,stock is in the 120 range,did u check the compression properly,with the motor cold,throttle open,if that's the true compression ratio,then you absolutely need to use premium fuel,also the proper mix ratio on a powervalve motor is 32:1,unless your running a high quality synthetic like amsoil ,then u can try 40:1,but I wouldn't recommend goin below that

  8. #8
    silvercrxsir's Avatar
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    Sounds like you were experiencing a lean-seizure condition on the lake

  9. #9

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    Yes the compression is on point. I have been mixing my gas with maxima castor 45/1. Could that be why the #1 cylinder is running lean?

  10. #10
    silvercrxsir's Avatar
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    It is possible,I would prob do a pressure test just to be sure because it can be a costly motor to fix,you can try 32:1 like the factory recommends also.a combination of the high compression and not enough oil could be the problem,just make sure you use premium fuel with the compression that high

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