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  1. #1
    PWCToday Newbie
    Join Date
    Jun 2009
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    Toronto Ontario
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    14

    GP800 not making full power

    I need some help with a problem I'm having.

    My ski started the season running normally and made full power. After 2 hours of running and 2 weeks of sitting it is topping out at 6500 RPM and used to do 7200. The ski starts and idles well and seems to have good power but the last part of the throttle range doesn't seem to do anything.

    Could this be a power valve problem? They are cycling normally after shut dowm but maybe they are gummed up and not opening completely at full throttle?

    I have tried fresh gas, new plugs and new fuel filter. A local mechanic suggested a new filter and spraying carb cleaner into the filter and running it through to see if there was any varnish that may have been dislodged from the filter and clogged the carb. I did that and ran a can of carb cleaner through it but it made no difference.

    I thought it was carb related before but I don't think it is now. It doesn't hesitate or run rough at any throttle speed and seems to be consuming gas as heavily as usual. With other 2 strokes when I've had clogged carbs, it usually stalls or runs rough and needs choke to run smooth. Not the case with the ski though.

    Plugs look clean and aren't fouled with oil. I do run Yamalube Watercraft oil only. I'm reading this stuff gums up power valves so maybe that's the issue?

    Any ideas are much appreciated! There really aren't any symptoms other than not making full power or reaching the usual top speed. I used to get 92 km/h and barely get 80 km/h now (on the dreamometer).

    All the local shops won't be able to look at it for a few weeks and I'd like to get it back in business sooner.

  2. #2
    Frequent Poster
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    Feb 2014
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    BC Canada
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    Re: GP800 not making full power

    Do you have a shop manual? Much experience wrenching and some selection of tools? The power valves could be an issue. They are on the exhaust side of the engine. Have you tried turning the power valve pulley by hand to full open and full closed? The covers are seen here right above the exhaust ports. With the engine in the ski and everything hooked up it can be tight to access. My 99 GP800 engine is out right now, so I can't really go have a look at it to confirm.



    The power valves are not difficult to work on once access is gained. If you do pull them apart to clean it is worth upgrading them to the new style keeper system so they won't fail and take out a piston.

    Last edited by keithb7; 07-12-2018 at 12:39 AM.

  3. #3
    PWCToday Newbie
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    Jun 2009
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    Toronto Ontario
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    Re: GP800 not making full power

    I do have tools but it's hard to get at both of them. One is almost covered by the exhaust manifold.

    Do you know how many degrees the pulley should rotate through to full open and closed positions? They are moving but I don't know if they are fully open or closed.

    I have the waveeater clips and coupler installed.

  4. #4
    Frequent Poster
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    Feb 2014
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    Re: GP800 not making full power

    I just took this video to show you full movement. Sorry I don't have a protractor on hand. Not sure of actual degrees.


  5. #5
    PWCToday Newbie
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    Jun 2009
    Location
    Toronto Ontario
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    Re: GP800 not making full power

    Thank you! I'll check it out. The more I think about it the more this makes sense.

  6. #6
    PWCToday.com Is My Home Away From Home WFO Speedracer's Avatar
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    Re: GP800 not making full power

    You must pull the exhaust manifold to service the power valves on an 800 motor.
    Y'all know me, still the same O.G. but I been low-key
    hated on by most these &^$$@s with no cheese, no deals and no G's, no wheels and no keys, no boats, no snowmobiles, and no skis, mad at me cause I can finally afford to provide my family with groceries


  7. #7
    Frequent Poster
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    Re: GP800 not making full power

    Agreed. You cannot pull the PV covers off with exhaust manifold in place. As seen here:


  8. #8
    Frequent Poster Dave in DE's Avatar
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    Apr 2016
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    slower lower Delaware
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    Re: GP800 not making full power

    Sounds like you better pull your power valve covers and check them. If you don't have wave eater clips or the enclosed style link on them you may have a pin that's fallen out of one of them. That would account for your rpm fall off. The pin may still be up in the linkage area right now. But if it falls into motor you'll have a mess.

  9. #9
    Frequent Poster
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    Re: GP800 not making full power

    I re-installed my GP800 engine today. I am now quite familiar with geting at those power valves. . It won’t be quick nor easy. Exhuast expansion pipe will have to come off. Release motor mount bolts. Lift engine up. Out of the ski enough to access exhaust manifold bolts. Remove exhaust manifold so you can access power valves. Quite a pain in the azz to get at.
    Last edited by keithb7; 07-15-2018 at 07:37 PM.

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