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  1. #1

    Join Date
    Apr 2011
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    3rd piston dead gpr1200 need help

    ok so i got a gpr1200 and this is the third piston i have put in my ski i bought the ski in pieces and no1 piston ring shattered so i rebuilt the engine took it for a run put about 30 hours on it then no1 piston guide pin pushed in letting the piston ring turn and catch on the exhaust port so thennnn i replaced that piston took it out again today put about 3 hours on it then lost compression in no1 cylinder removed the head and yet again piston had a hole blown through it on the exhaust side now I'm over this bulshit and wonder if i should (A) grind down the power valves (B) remove the power valves all together or (C) buy non power valve cylinders someone give me some ideas cos I'm over this power valve bulshit


  2. #2

    Join Date
    Apr 2006
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    South MS
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    Post pics of the damage. Maybe someone can help you. I'm not sure why your blaming the power valve?

  3. #3
    JKR1300's Avatar
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    hole burnt thru the piston top = serious lean condition

  4. #4

    Join Date
    Jun 2008
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    Hillsborough, North Carolina
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    I'm thinking that you need to give us a little more history to help everyone understand your situation.

    Did you pressure test it after the repairs? What about carb rebuild? Do you have the wave eater clips installed? etc...

    Thanks, I know your pain though!
    Last edited by mrtinker; 01-02-2012 at 12:57 PM. Reason: Literacy!

  5. #5

    Join Date
    Apr 2011
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    australia
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    ok so i had all new gaskets pistons etc I'm thinking now tho since i did the rebuild i disconnected the oil pump and running 40;1 premix so i think it must be running way to lean on the high speed jets . If that is the case I'm not going to bother pulling down my carbs and re-jetting I'm buying a set of novi 48 carbs with a custom manifold with some flame arrestors. And with the carbs will be getting a set of triples some carbon reeds a riva ignition and getting barrels bored out to 1300 cylinders with sleeves installed

  6. #6

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    Jul 2008
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    cape cod
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    195
    Wow those are some big changes,expensive too

  7. #7

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    Apr 2006
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    Quote Originally Posted by cuda167 View Post
    Wow those are some big changes,expensive too
    That's what I was thinking. If the stock 1200 keeps blowing a cylinder, you will really have your hands full with trying to keep a triple pipe together.

  8. #8

    Join Date
    Apr 2011
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    australia
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    yea i think my main problem was the stock carb jets were making ski run way to lean when i changed it to premix and possibly could have blockage in one of the carbs but could not be bothered looking since i have new ones ready to bolt on

  9. #9
    PolarisNut's Avatar
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    Dec 2006
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    Lower Michigan
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    Quote Originally Posted by ryancoggo View Post
    yea i think my main problem was the stock carb jets were making ski run way to lean when i changed it to premix and possibly could have blockage in one of the carbs but could not be bothered looking since i have new ones ready to bolt on
    I think you have bigger issues than that. Just switching to premix won't make your ski run noticeably leaner that it was with oil injection. I'd look elsewhere for your issues. Try listing exactly what is done to your boat. If you have the stock airbox removed, and the stock jets in your carbs, that is a problem.

  10. #10

    Join Date
    Apr 2011
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    stock air box was still on but I'm pretty positive that i had the stock jets in the carbs cos person before hand had a few things done to ski but I'm pretty sure he didn't re-jet the carbs. I probs have a blockage in that carb causing it to run lean i know its not from the cooling system already checked that had lots of water pressure and no blockages so then i thought it was the power valve that chewed out the piston but i checked that and even with the power valve disconnected it still doesn't enter past the cylinder wall so thats why I'm pretty sure that cylinder was running lean. Blew a hole threw the exhaust side and on top of the piston on the exhaust side aswel

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