Ultra 250X New rebuild, good boost, low power. 40MPH Max
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  1. #1
    PWCToday Newbie
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    Ultra 250X New rebuild, good boost, low power. 40MPH Max

    I just rebuilt a 08 250x. Cylinders Recoated, New Pistons / Rings, Head fully done, all new valves. Supercharger rebuilt. Jet drive inspected. Runs well, but has low power / max speed. I get 11 psi boost on the display. I was suspecting the BOV being faulty, but the sensor for the gauge is after the intercooler. I removed and flushed the intercooler with gas. Tried running with the seat off, and no help. Its not cavitating, just not getting near what I should. I read a lot of posts about leaking hoses etc, but I think I would see lack of boost if that was the issue. Everything is stock. The valve cover does not have the vents.
    I do have a spare parts machine, so can swap out some parts.
    Any ideas?
    Thanks

  2. #2
    PWCToday Newbie
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    Re: Ultra 250X New rebuild, good boost, low power. 40MPH Max

    cam timing?

  3. #3
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    Re: Ultra 250X New rebuild, good boost, low power. 40MPH Max

    Not likely but a possibility. It runs too well! I did take the BOV and Bypass valve from the other machine. I also cleaned the injectors. Its a little better now, close to 50MPH, just not what it should be.

  4. #4
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    Re: Ultra 250X New rebuild, good boost, low power. 40MPH Max

    When I replaced the bypass valve I noticed that the old one would 'vent' at idle. However the other one also did this. This didn't make sense to me, but again the boost shows 11PSI on the display when the revs are up.

  5. #5
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    Re: Ultra 250X New rebuild, good boost, low power. 40MPH Max

    What’s it supposed to make for boost PSI? Could also make some plugs up and leak test the intake setup from supercharger outlet to the throttle body. Make sure it’s not leaking somewhere.. but it starts and runs great? Spark Plugs all same colors?

  6. #6
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: Ultra 250X New rebuild, good boost, low power. 40MPH Max

    4 strokes are not my thing, and as a watercraft mechanic I only changed
    the oil, but I was a motorcycle mechanic first, that got roped into working
    on Jet Ski's because nobody else wanted too.

    Quote Originally Posted by SxrJosh View Post
    Spark Plugs all same colors?
    Generally all 4 plugs should be white, if they have any color on 1 or
    more cylinders that could warrant inspection.

    When rebuilding 4 and 6 cylinder Kawi's, it was easy to catch and
    accidentally bend an oil ring during assembly.

    A compression test would be nice, and all cylinders should be within
    a few psi at the most.

    But a percentage leak test is the best way to evaluate a top end.
    With a percentage leak test you can inspect the rings, intake and
    exhaust valves all at the same time.


    A common problem with cam timing is to have all the marks lined up,
    and when you install the cam chain tensioner the cams rotate back
    1 tooth.

    On shim under bucket I used to measure stem height before the head
    was completely disassembled. Did you inspect the valve clearance before
    or after the top end was reassembled?

    Have you inspected the engine oil level after you were on the water?



    Bill M.

    Hope this is helpful.
    Horsepower == Speed, RPM != Speed



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