Yamaha 65U & 63M
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  1. #1
    Top Dog Lakeside518's Avatar
    Join Date
    Jun 2007
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    Clifton Park-Albany area, NY
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    Yamaha 65U & 63M

    Harry I just shipped out my intake manifold, carbs and head off my 1100 waveraider. Here's my question.

    Is it possible to install 65U cylinder with pistons bored .50 over on 63 cases? Will they clear the cases without boring?

    Will the Triple 38M carbs support it? I'm thinking about doing this if possible and asking you to jet my carbs for a 65U bored .50 over.

    Will this run better then the big bore kit 1130 setup? How reliable is this?

    Let me know

    Thanks

  2. #2
    Tech Guru Resident Guru
    Join Date
    Feb 2002
    Location
    Fort Mohave, AZ
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    65
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    1,150

    Re: Yamaha 65U & 63M

    While the 1200 cylinder will bolt right on to 1100 cases, we don't recommend it (in the world of today's 91 octane fuel). The 38 carbs can feed the 1200 cylinder okay, but the problem is the ignition curves.

    The 1200 igntion has seperate curves for each cylinder that makes for better performance of the 1200 cylinder, as well as better prospects of being pump gas safe.

    If you have the 1100 ignition, you will get the best performance results with an 81-82mm 1100 cylinder ... I know it seems like the 84mm 1200 cylinder should be an obvious increase on that motor, but repeated on-water tests have shown otherwise.

    Respectfully, Harry Klemm



    Quote Originally Posted by Lakeside518
    Harry I just shipped out my intake manifold, carbs and head off my 1100 waveraider. Here's my question.

    Is it possible to install 65U cylinder with pistons bored .50 over on 63 cases? Will they clear the cases without boring?

    Will the Triple 38M carbs support it? I'm thinking about doing this if possible and asking you to jet my carbs for a 65U bored .50 over.

    Will this run better then the big bore kit 1130 setup? How reliable is this?

    Let me know

    Thanks
    Unless otherwise stated, responses to all forum posts are based on my personal experiences working within the PWC industry, and developing high performance PWCs since 1987.

    www.groupk.com

  3. #3
    PWCToday Newbie
    Join Date
    Apr 2017
    Location
    Texas
    Posts
    5

    Re: Yamaha 65U & 63M

    Is that because the port timing is "hotter' on the 65u cylinders? I don't understand what ignition timing has to do with a displacement increase.

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