SXI Pro - Trouble coming on the pipe
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  1. #1
    PWCToday Guru
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    SXI Pro - Trouble coming on the pipe

    Been a while....have a new build I have been working on and am encountering something strange which i am looking for input on. Below are the specs and issue....looking for educated input

    Setup:
    - 2001 SXI pro
    - milled head for 92 octane, rest of the engine is stock
    - Boyesen dual stage fiber reeds, original i-body 40mm dual carbs with 2.0 N/S, 80g springs, 75 pilots / 150 mains. Choke & choke plates still hooked up. Tau Ceti flame arrestors.
    - Factory Pipe limited pipe, water screws set at: top - 3/4 turn out, middle - 1/8 turn out, bottom - 1/8 turn out. water lightly sizzles on chamber after ride.
    - Water routing follows factory's "race" setup (with temp sensor bi-passed), electrical wires for temp sensor is still currently hooked up
    - 9/17 big hub swirl Skat impeller, 650sx outlet nozzle (83mm)
    - Riding at sea level with temperature in the 70s/80s.

    Issue:

    When first starting the ski, the first 1-2 minutes feel great. Ski and pipe seem to hit powerband between 1/4 to 1/2 throttle. Ski wakes up and you can tell the powerband of the pipe is occurring. After the first 1-2 minutes of riding....the ski will not hit the powerband naturally. Only if the pump comes unloaded will the ski hit the power band. After the pump comes unloaded, when the ski hits the powerband and the pump again hooks up, the ski will stay in the powerband for a run....but if you let off the throttle and again hit the throttle....ski will not naturally hit the powerband. This problem seems to get incrementally worse the longer the ski is ridden.

    Questions:

    1. Based off everyones experience, do we think this may be a jetting issue? One of the next things I plan to try is to try larger pilots potentially....and larger mains...but did not have larger pilots or mains on hand to try.
    2. Does this sound like a pipe issue? If so, any thoughts?
    3. The bi-passed temp sensor.....would the electrical wires still being hooked up cause this? (since no water is being routed through the sensor)


    Thanks for any input.

  2. #2
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: SXI Pro - Trouble coming on the pipe

    The FPP limited pipe is about 2" shorter than normal, and on
    a SXI Pro cylinder will need about 7000 to 7200rpm.

    My guess is the impeller is too large for that pipe and exh port
    timing, and it runs decent until the pipe heats up.


    Bill M.

    Have you tested the compression?
    What are the fuel screws set to?
    Did you test the pop-off?
    How long ago were the carbs rebuilt?
    Last edited by wmazz; 07-19-2022 at 04:16 AM.
    Horsepower == Speed, RPM != Speed



  3. #3
    Top Dog JC-SuperJet's Avatar
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    Re: SXI Pro - Trouble coming on the pipe

    The Engine might have an Air Leak causing it to run Lean after the Aluminum Metal Components heat up and expand allowing gaps for Air Leaks.

    How old are the Crank Seals? How old are the Gaskets?

    Did you bother to do an Air Leak-down Test on the Engine before putting it back into Service?

    Most People ignore this Critical Test and then end up with Carburetion issues that can't be solved until the Air Leaks are found and repaired.

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