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  1. #1

    1998 GP800 compression issue. What to do next?

    Hi all, I have just checked the compression on my GP800 98 model and got 125 front and nothing on back and am woundering what I should do next as I was thinking to have a look at the power valves? I have a workshop manual and was really hopping someone has had this issue and can give me an idea on what it could be and how to fix it?

    Any advice and help would be appreciated as it comming into summer and jetskiing so I want to sort ASAP.........

    Help please............


  2. #2
    mudslanger's Avatar
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    It sounds like you have serious cylinder trouble the best thing to do is pull the head and look in the cylinder to see what has gone wrong with the piston and cylinder.

    Good luck let us know what you find.

    Welcome to the forum.

  3. #3
    Yamaha artisan Cutlass's Avatar
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    I agree. Pull the head and take a look at the destruction. Then you'll need to figure out why it destroyed itself, fix that problem, and rebuild the engine.

  4. #4
    Yep, I'm taking to motor out tonight and then off with the head and see what has happened ggggrrrrrrrrrrr. Will post a photo if there is something obvious that sticks out, anyway it's done 155hrs and proberly due for piston and rings anyway?

  5. #5
    Ok, cylinder was toast and piston overheated which blew a hole in the side so have put new cylinder and piston in and have cleaned power valves and I carb kitted it also so she is fresh and just put motor back in today and fired up straight away and sounds mint But, yes but the engine is reving hi and I woundering if adjusting the power valve cables will fix this as I don't think its set right?
    What do you think as I'm thinking to adjust the power valve cables tomorrow, if anyone knows how to set them up to be in the right position would be a great help?

  6. #6
    If I can work out how to upload a photo I will because it's impressive for sure
    Quote Originally Posted by mudslanger View Post
    It sounds like you have serious cylinder trouble the best thing to do is pull the head and look in the cylinder to see what has gone wrong with the piston and cylinder.

    Good luck let us know what you find.

    Welcome to the forum.

  7. #7

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    Quote Originally Posted by NZ Jetski rider View Post
    Ok,........and fired up straight away and sounds mint But, yes but the engine is reving hi ......

    You did not tell us what it was that caused all of your problems in the first place. I know you lost a cylinder and piston, but why? I get nervous responding to questions when I do not know all the facts. For instance, did you check for a rear seal leak when you tore it down? Did you do a leak down test when you put it back together? A leaking seal will cause your engine to rev high, or even run away. It can also cause you to loose a piston and cylinder by running lean.

    Sure, it is possible that your carbs need to be adjusted, especially since you went through them and more than likely you did not set them exactly back to where they were. It could be something as simple as adjusting your idle adjustment.

    I would not think that it would be a valve problem.

    I.

  8. #8
    Yamaha artisan Cutlass's Avatar
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    Quote Originally Posted by NZ Jetski rider View Post
    But, yes but the engine is reving hi
    It'll idle higher out of the water then in it. Mine revs about 3000rpm out of the water and about 1200rpm in the water. But like salty said, a air leak or misadjusted idle screw can also cause it to idle really high.

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