1994 square nose Yamaha Superjet bogs/cuts out
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  1. #1
    PWCToday Newbie
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    1994 square nose Yamaha Superjet bogs/cuts out

    Hello, recently I purchased a superjet. I took it out in the water line ran great no problems till about 30 min in I noticed I had broke 3/4 motors mounts. And Iím still a beginner so was not riding hard. I took to a shop got all 4 replaced he went to tank test and it back fired on start up causing the water box to destroy. Once replaced he started up and he said it only goes about 1/3 throttle then bogs/cuts out. He claims to only have lifted up engine only 1/2 inch when replacing mounts. I took to water thinking maybe needs to clear out still nothing. It start up right away and Idles perfect and will rev good till 1/3 throttle then bog/cut out. I took it back and we tired a carb rebuild no help. As well as replacing spark plugs still no help. Do you guys have any clue what could be causing this. Iím new to the forems and couldnít find any related in search bar.
    thanks again Gage

  2. #2
    Top Dog JC-SuperJet's Avatar
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    Re: 1994 square nose Yamaha Superjet bogs/cuts out

    Backfires can damage the Intake Reed Petals and also blow the Crank Seals.

    Inspect the Reeds.

    Pressure test the Engine for 10 minutes @ 8 psi to find any Air Leaks which would cause the Engine to run very Lean.

  3. #3
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    Re: 1994 square nose Yamaha Superjet bogs/cuts out

    Thank you I’ll try that!

  4. #4
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: 1994 square nose Yamaha Superjet bogs/cuts out

    Quote Originally Posted by Gage_Anderson View Post
    I took to a shop got all 4 replaced he went to tank test and it back fired on start up causing the water box to destroy.
    Does your SJ have a fuel primer? Water boxes blow up
    after the engine is loaded up and backfires. They explode
    because there is fuel inside the waterbox. But if it was loaded
    up, and the tech used starting fluid that is a common way to
    get the waterbox to explode.

    I saw a SeaDoo rider having problems starting his engine one
    time at a lake. So he squirted starting fluid down the carb, and
    with confidence the engine would start, he put the seat on,
    and sat on his ski. The water box blew apart immediately after
    he tried to start it, and the explosion lifted him and the seat
    about 6" off the hull, despite the seat being latch to the hull

    Another problem related to 44's is damage to the fuel pump
    ck valve and sometimes the fuel pump diaphragm.

    But, if the engine was loaded up, how did it get loaded up
    in the first place?? My guess is the engine has a tendency
    to be hard to start. If there is a fuel primer, that confirms
    it was hard to start in the past.


    Bill M.

    Motor mounts break from wake/wave jumping.
    Last edited by wmazz; 07-21-2022 at 02:23 AM.
    Horsepower == Speed, RPM != Speed



  5. #5
    PWCToday.com Is My Home Away From Home john zigler's Avatar
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    Re: 1994 square nose Yamaha Superjet bogs/cuts out

    Back fires can also be a timing issue. Bad CDI, loose Stator coil, sheared flywheel key, etc.
    RCJS also doing business as WATCON
    608-743-1305 9am to 5pm CST m-f
    email watcon@watcon.com

    Please visit our web site

    new parts / products / services www.watcon.com
    thank you

    Please check out and like WATCON on Facebook

  6. #6
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: 1994 square nose Yamaha Superjet bogs/cuts out

    Quote Originally Posted by Gage_Anderson View Post
    I took to water thinking maybe needs to clear out still nothing. It start up right away and Idles perfect
    and will rev good till 1/3 throttle then bog/cut out.

    I took it back and we tired a carb rebuild no help.
    If there is an exhaust leak, or an exhaust hose has a blister
    inside the hose, each of these possibilities would prevent
    the ski from planing at wot.

    Did a water line come off while you were riding it with those
    broken motor mounts?

    If so, there may be some other problems too.


    Bill M.
    Last edited by wmazz; 07-21-2022 at 03:19 PM.
    Horsepower == Speed, RPM != Speed



  7. #7
    PWCToday.com Is My Home Away From Home Myself's Avatar
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    Re: 1994 square nose Yamaha Superjet bogs/cuts out

    Quote Originally Posted by wmazz View Post
    Did a water line come off while you were riding it with those
    broken motor mounts?

    If so, there may be some other problems too.


    Bill M.

    WAIT a minute Bill........are you suggesting a person should actually remove the hood (or seat) and inspect things before every ride????? Now that's just absurd......you might find broken motor mounts or something!
















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