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compression 96 GTX

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  • #16
    Re: compression 96 GTX

    OEM pistons in Rotax motors of that vintage use an L top ring that better uses compression to force the ring tight to the clyinder wall. If a Rotax motor with oem rings is blowing 5 lbs lower than it should, there will be damage, however mild, but still damage, or the machinist should be selling used cars for a living.

    If you use aftermarket pistons and rings, the gap widens between acceptable and not acceptable standards.

    I consider 5 lbs lower the maximum amount of difference that is acceptable in an oem Rotax application.
    Your opinion may vary.

    A machine shop or jetski/motorcycle shop that bores clyinders can vary drastically from one shop to another in the precision and tolerances of the work or their equiptment. This can drastically effect the lifespan of an engine's ability to seal the rings in the clyinders due to the quality of a boring and honing operation.

    I only use the best machinist and he owns the best equiptment, a German made boring bar and a Sunnen precision honing machine, both refitted with tooling and honing stones and oil on a regular basis, for all of my in-house rebuilds. I usually do not see 2 lbs difference between clyinders on engines that we rebuild the clyinder for using oem Rotax pistons and rings.

    I do not consider a racing engine any more important that the average customers engine when it comes to precision machine work on the clyinders.
    Bill O'Neal <br>
    WCM
    <a href="http://www.watercraftmagic.com"

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    • #17
      Re: compression 96 GTX

      I am glad to hear that. It just scared me when the ski just stopped and would not start the 12V low started flashing when it stalled and the starter would only turn the motor over about a 1/4 of a turn then by the time i got it back to the dock it fired up again and ran for a bout 5 min then the same thing happend. i thought it was the battery not charging thats why i changed the rectifier or do you think the motor was siezing from lack of fuel?

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      • #18
        Re: compression 96 GTX

        I have no way of knowing for sure from here, but you just described a siezed motor.
        Shuts off all by itself at speed, piston grows from heat and sticks, motor won't turn, piston cools off and shrinks, motor starts. That is a classic description of a high speed piston siezure.
        Bill O'Neal <br>
        WCM
        <a href="http://www.watercraftmagic.com"

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        • #19
          Re: compression 96 GTX

          should i make the motor a little more rich or could there have been a problem with fuel making it to the pto carb? what way to turn the screw to make motor burn more on the rich side? Bill thank you so much for taking the time to help me out i am getting to the end of my rope with this ski. All i want to do is to have some fun on it before the snow flies.

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          • #20
            Re: compression 96 GTX

            Needle adjusters always add fuel when you turn them counterclockwise.

            The rear carb is connected directly to the front carb and if the front carb has fuel, so will the rear carb if both carb's internal filters are clean.
            Bill O'Neal <br>
            WCM
            <a href="http://www.watercraftmagic.com"

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            • #21
              Re: compression 96 GTX

              I have cleaned both filters and have the adjustment screws about 1 turn out the ski starts up very fast and i dont even need the choke. This would lead me to believe that it is ajusted right and hopefully ready to ride. If anyone comes up with anything at all to check before i head out this weekend please let me know. Thank you for the help

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              • #22
                Re: compression 96 GTX

                one more thing should i maybe turn the high speed screw out a little right now it is at 0 turns out? How could i tell if it was all the way out and not all the way in could that cause it to lean out at high speed?

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                • #23
                  Re: compression 96 GTX

                  One turn out ? If those high speed adjusters are 1 turn out, that thing will run way too rich, unless of course you have an air leak into the motor.

                  OEM high speed adjusters settings, closed to 1/4 turn out from closed.
                  Low speed adjusters between 1.25 turns out to 1.75 turns out.
                  Bill O'Neal <br>
                  WCM
                  <a href="http://www.watercraftmagic.com"

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                  • #24
                    Re: compression 96 GTX

                    Bill i am sorry you missunderstood what I was saying the speeds are one turn out and the high speeds I think are cloesed all the way clockwise?? should i have the lows out more than what the manual says. the book I have says one turn out +/- 1/4 turn. Maybe that could be my problem?? I trust what you say more than than what the book says.

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                    • #25
                      Re: compression 96 GTX

                      On my gtx it says in book that the pto carb should be 1/4 out on high and 0 out on mag carb. Thats how i got mine it seem great. Lows are little over 1 out .

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                      • #26
                        Re: compression 96 GTX

                        I thought both carbs had to be set the same??

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                        • #27
                          Re: compression 96 GTX

                          Exact carb setting may be the same - but may be different. All specs are +/- 1/4 turn to fine tune.
                          SBT Tech Support is here to help with your problems.
                          We try to answer each question quickly and accurately.
                          Please do not use Private Messaging for Tech Support, use the forums.

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                          • #28
                            Re: compression 96 GTX

                            Do the high speed ajusters only controle the fuel at WOT? What rpm range do they controle? When i was braking the motor in it ran fine at 1/2 - 3/4 throtle but the pto plug only had a little brown on part of it and the rest was still white because they were brand new plugs and were run for 1.5 hours the mag plug was a nice light brown the hole thing. Could the high speed ajusters being all the way in like the books says cause it lean out at WOT to the point that it shuts ski off?

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                            • #29
                              Re: compression 96 GTX

                              Read the tech article on carb tuning.
                              SBT Tech Support is here to help with your problems.
                              We try to answer each question quickly and accurately.
                              Please do not use Private Messaging for Tech Support, use the forums.

                              Comment


                              • #30
                                Re: compression 96 GTX

                                If you want the rear sparkplug to darken up, open the rear carb high speed adjuster a bit futher open.

                                The high speed adjuster and jet circuits start adding fuel as soon as the butterfly opens enough to uncover the high speed diffuser. In laymen's terms, that means about 15 % open.
                                Bill O'Neal <br>
                                WCM
                                <a href="http://www.watercraftmagic.com"

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