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Thread: 550 dilemma

  1. #1
    PWCToday Guru treys599's Avatar
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    550 dilemma

    Long story short, a friend busted up my ski pretty good, so I pulled the motor out (1990 550sx) it sat in my garage for a week then I put the motor in my 440. The motor ran pretty good in the old hull and even after the crash it made it home without any problems. Once I put it in my 440 though it runs like junk, doesn't want to rev, bogs at low throttle, bogs transitioning to full throttle and bogs at full throttle after a few seconds of WOT. Ive tuned pp's before so ive had some experience with the round body carbs but no input makes any difference on this one. Has good compression, cylinder walls look good and doesn't seem to have an air leak. I pulled the intake manifold and carb off to check it out, its different than my other 90 550sx's stock carb. Inside looks ok, nothing jumps out as being the culprit, pretty normal wear and pretty normal condition for a JS. Starting to hate these things...but ive got too many to quit now
    Any ideas appreciated, Thanks.

    PS what carb is this, venturi is different from all others ive seen.
    IMG_7494.JPGIMG_7493.JPGIMG_7492.JPG

  2. #2
    I dream skis
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    Re: 550 dilemma

    Im reading that you have the 440 carb on the 550. If so, that’s your issue. Put the 550 carb on the 550 motor. Post your results

  3. #3
    PWCToday Regular
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    Re: 550 dilemma

    That looks like a a mikuni 38 bn.

  4. #4
    PWCToday Guru treys599's Avatar
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    Re: 550 dilemma

    the carb is 44mm, it came on the engine when I got it. It is the same carb that has been on the engine the entire time ive owned it. I meant to say I put the motor in my 440 hull, I swapped over the 550 ebox and the complete 550 motor (exhaust, carb everything it needs to run). Unlike all other round body carbs ive come across, this one does not have a booster, instead it has a bunch of little holes all around the venturi where the gas/oil sprays into the venturi from.
    Last edited by treys599; 05-29-2018 at 10:37 PM.

  5. #5
    PWCToday.com Is My Home Away From Home
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    Re: 550 dilemma

    green racing specialties annular booster carb mod.

  6. #6
    PWCToday Guru treys599's Avatar
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    Re: 550 dilemma

    Quote Originally Posted by restosud View Post
    green racing specialties annular booster carb mod.
    Thank you, is it worth messing with or should I just put a stock 44mm carb on?

  7. #7
    PWCToday.com Is My Home Away From Home
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    Re: 550 dilemma

    Decent racing carb for back then but quite often had low end problems.
    Try a stock 44 or sbn or a Walbro wda.

  8. #8
    PWCToday Guru treys599's Avatar
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    Re: 550 dilemma

    Makes sense, it would stumble on low end but ran like a bat out of hell on the top end. I went ahead and rebuilt my stock 44 using a genuine mikuni kit, new intake gaskets and it runs good out of water now, it didnt even do that with the other carb. Ill have to put it in the lake later this week and see how it does.

  9. #9
    PWCToday.com Is My Home Away From Home
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    Re: 550 dilemma

    Yeap,all 550 sound good out of the water.sometimes a different story once in water though.

  10. #10
    PWCToday Guru treys599's Avatar
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    Re: 550 dilemma

    Quote Originally Posted by restosud View Post
    Yeap,all 550 sound good out of the water.sometimes a different story once in water though.
    Happens every time haha.

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