98 Sea Doo GTX Limited High RPMs out of the water, Low RPMs in the water
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  1. #1
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    98 Sea Doo GTX Limited High RPMs out of the water, Low RPMs in the water

    I purchased a 98 Sea Doo GTX earlier this year. The first few times we took it out, it would get to 45 miles per hour than hit another gear/band. We could get a speed of between 59-61 miles per hour. Recently it won't hit that next level. I can only get it to 5400 RPM or 35 miles per hour. I have cleaned the rave valves, changes the spark plugs and we use ethanol free gas. If I replace the bellows on the water regulator, will it correct this problem? Is there anything else that I can check to correct this problem? Thank you.

  2. #2
    Resident Guru SpitAndDirt's Avatar
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    Re: 98 Sea Doo GTX Limited High RPMs out of the water, Low RPMs in the water

    You have a 951 Time Bomb. Any 951 over at 150+hrs needs to be considered to be running on borrowed time. The engine MIGHT be telling you that it's time to get a full upper engine rebuild done, if not a complete engine overhaul.

    To answer your question about the water box regulator bellows: The bellows normally isn't the problem, it's that the STEEL spring clamp at the bottom of the bellows rusts away and doesn't provide a adequate seal. If it leaks water internally, you may not be able to hit full WOT Rpms. Small adjustments of the water regulator cap can help to achieve maximum RPM when everything is operating correctly. Such a significant drop in Rpm's is definitely something that needs to be investigated.

    To effectively diagnose the problem, we need to know the number of hours on the ski. What is the history? How was it maintained before? Since you are in Colorado, what is the altitude that you operate the ski at? Is the engine original? Have you performed a compression check? Have the carbs been removed and the tiny internal filters cleaned? Was the engine rebuilt? Have all the fuel hoses been replaced with ethanol resistant fuel hose? Is your water box regulator adjusted so that the red adjustment screw is flush with the black cap?

    What about the jet pump? Condition of the wear ring? Has the jet pump oil been checked or changed?

    The fact that you are only hitting 35 miles per hour is a HUGE red flag to investigate all possible culprits.

    In perfect working order and in stock form, you should definitely be hitting consistent 59-62mph speeds.
    Last edited by SpitAndDirt; 09-30-2020 at 06:16 PM.
    "The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed."

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  3. #3
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    Re: 98 Sea Doo GTX Limited High RPMs out of the water, Low RPMs in the water

    Thank you for the response. I will check those items.

  4. #4
    PWCToday.com Is My Home Away From Home Myself's Avatar
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    Re: 98 Sea Doo GTX Limited High RPMs out of the water, Low RPMs in the water

    LOTS of truth in that timebomb statement above.
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  5. #5
    PWCToday.com Is My Home Away From Home john zigler's Avatar
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    Re: 98 Sea Doo GTX Limited High RPMs out of the water, Low RPMs in the water

    I am going to guess, standard SeaDoo grey fuel lines breaking down, carbs gummed up, running lean.

    Go through the fuel system completely, replace ALL lines, fuel select, rebuild carbs, and fuel pump with genuine mikuni brand parts. Replace needle and seats as well.

    Could also be voltage regulator. You can unplug it and then re-test. (see if it goes up to speed / rpms)

    Sorry I also agree the 951 is not the most reliable engine SeaDoo made....
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  6. #6
    Resident Guru SpitAndDirt's Avatar
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    Re: 98 Sea Doo GTX Limited High RPMs out of the water, Low RPMs in the water

    Its not so much "not-reliable" but high-maintaince because it runs at the bleeding edge if performance for its size.

    Personally, since I rebuilt my first 951, I thought it was a decent trade off. When it runs, it runs very well and very fast.

    Its just that SeaDoo didn't bother to inform the consumer. How else you gonna remain in business if you aren't selling new units? Double edged sword. Now that I have all my 951 kinks worked out and know what my inspection/rebuild schedule SHOULD be, ill be keeping my 99XPL indefinitely. Or as long as oil and gas are still sold ....

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    "The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed."

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    Rides: 2 x 96XP // 99XPL // 02RX Currently rebuilding
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  7. #7
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    Re: 98 Sea Doo GTX Limited High RPMs out of the water, Low RPMs in the water

    I was getting a 12 volt low warning, so I had a shop put in a voltage regulator/rectifier. Could that be the problem?

  8. #8
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    Re: 98 Sea Doo GTX Limited High RPMs out of the water, Low RPMs in the water

    I took the water box regulator apart and the only spring was the one under the cap. I pulled the clamp of. Removed the black cap. Unscrewed the long screw from the bottom and removed the bellows assembly. The bellows was secured with a pinch clamp. Once you remove the bellows is there supposed to be a spring there?

  9. #9
    Resident Guru SpitAndDirt's Avatar
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    Re: 98 Sea Doo GTX Limited High RPMs out of the water, Low RPMs in the water

    Per the shop manual: All models with a 947 engine, the rectifier/regulator is integrated in the MPEM.

    So are you saying the shop installed a NEW MPEM? Or did someone try and connect some sort of external one?

    What you are referring to as a "pinch clamp" is what I called a spring clamp.

    In the picture below, both the red dots AND blue dots indicate where the pinch clamps are installed. The blue dots are the screw secured stainless steel clamp, and the red dots are the regular steel clamp that requires pliers to remove.

    The idea is that at low speeds, more water is directed to the tuned pipe and at high speeds, LESS water is fed to the tuned pipe.

    But this wouldn't have that much affect on you losing 2000 rpms.
    Attached Images Attached Images
    Last edited by SpitAndDirt; 10-01-2020 at 02:34 PM.
    "The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed."

    -Robert M. Pirsig, Zen and the Art of Motorcycle Maintenance

    Rides: 2 x 96XP // 99XPL // 02RX Currently rebuilding
    I love my CanDooPro! Take that stealerships!! www.candoopro.com

  10. #10
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    Re: 98 Sea Doo GTX Limited High RPMs out of the water, Low RPMs in the water

    Thank you for the information. Because the rectifier/regulator is integrated with the MPEM, they installed in external one with new wiring.

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