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  1. #1

    Need opinions on rebuild 65u

    Hi guys, I am back. I have the 65u in a gpr hull. Started running rough and checked compression....60, 100. 90. Pulled the head and one piston damaged #1 and one dome damaged on the head #3. I think the damaged head was from the previous owner. Ok, question, by looking at the pics, does the cylinder need to be bored? How deep can the marks in the cylinder be that it just cant be honed?

    If I send the head to be milled, can they fix the dome or should I just look for an aftermarket head.

    Another question does cylinder porting increase top end or just low and midrange? I use my ski in the ocean so low end is not to important.

    Can I change just one piston or should I just get a set of aftermarket pistons?

    I did 58 on gps before this mishap.

    Anything else you can see from the pics?

    Any used milled stock heads around? Any ported cylinders? Any 150psi heads out there?

    Thanks!!!!!
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  2. #2
    Adam's Avatar
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    Wink

    Lean seizure , probably caused by damage check valves in the fuel pumps !
    If the bore is undamaged ,you could sand any piston residue off the bores and replace the piston and rings. But you "must" check the fuel pumps for damage to the checkvalves or this will happen again first time you ride it !

  3. #3
    Mpeavler's Avatar
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    1. Start fresh and bore/hone the cylinder with all the new slugs and equal bores.

    2. VERY VERY lean...carb rebuilding time and if not stock ...different jetting maybe needed

    3. 150 PSI will give more all around power....mostly bottom/mid unless you prop for more top end speed.

    4. 65U in a GPR hull.....

    5. Porting is all around power...and well worth the money IMO if your into power/speed.

  4. #4
    bullisland's Avatar
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    Quote Originally Posted by Mpeavler View Post
    4. 65U in a GPR hull.....
    +1

    Theres a guy that does GREAT work on these that Flying Scottsman lead me to (Tim @ Z Force Racing). Let me know if you want his info. He just did my fresh bores and matched pistons for me for my top end rebuild. Great craftsmanship and guy to deal with.

  5. #5
    Yes, I know it doesn't make much sense....65u in a gpr hull. It used to be an 800 and the previous owner stuffed the 65u engine in it. I need to get about 62 - 64 out of this rig or I am going to get a 13. If I can get that speed out of this 65u I would rather keep my ski. If after the head, porting and carbs I cant get 62 - 64 I think I would just put it back stock and sell to get a 13.

    Thanks.

  6. #6
    If I send this head in the pictures to get milled, can they fix it also? Or, do I need a new head?

  7. #7
    Flying Scotsman's Avatar
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    Get a new head lol.....
    Raised comp and porting will get you to your goal.
    Your talking another 30 hp or so .

  8. #8
    krispaintballz's Avatar
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    Quote Originally Posted by bullisland View Post
    +1

    Theres a guy that does GREAT work on these that Flying Scottsman lead me to (Tim @ Z Force Racing). Let me know if you want his info. He just did my fresh bores and matched pistons for me for my top end rebuild. Great craftsmanship and guy to deal with.

    Timmy Zarnsdorf (I think that is how you spell it). Nice guy actually spoke to him couple weeks ago with pat's project.

  9. #9
    bullisland's Avatar
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    Quote Originally Posted by krispaintballz View Post
    Timmy Zarnsdorf (I think that is how you spell it). Nice guy actually spoke to him couple weeks ago with pat's project.
    Yessir thats him! (just checked UPS and parts were delivered )

    BTW, thanks again scotty!

  10. #10
    Flying Scotsman's Avatar
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    Tims a great guy and knows about all the watercraft not just Yamaha.

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