JS550 Fuel Issue
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  1. #1
    Frequent Poster sorejo's Avatar
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    JS550 Fuel Issue

    So I just picked up a '86 550 and am having issues starting it. I have poured gas directly into the carbs and it runs till it burns off the fuel I add. The engine is completely stock and it has the Mikuni BN44 Round Body carb. It also doesn't have a primer. I have attempted to bypass the fuel filter with a Bic pen cut... it pulls fuel but there are also always air bubbles. I have also tried running a hose from the reserve pickup straight to the pen and then to the carb. It didn't pull air in at all but it also didn't run... I need to rebuild the carbs but do I need to replace the hoses? I also tried putting a bottle of gas with a gear oil tip on it and when I put some pressure on the bottle it leaks from the layers (behind the plastic cover and behind the next metal layer) of the front of the carb. Do I need a rebuild kit and what can I do to stop the leak from the plastic?
    1986 Kawasaki JS550

  2. #2
    PWCToday.com Is My Home Away From Home Myself's Avatar
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    Re: JS550 Fuel Issue

    Sometimes the fuel pickups crack up towards the top. Submerse it in a bucket and blow air into the pickups to check for air bubbles. Yes, sounds like a carb rebuild is in order. Somebody has probably opened up the carb and torn some gaskets. There is a flat o'ring behind the plastic center cover.
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  3. #3
    Frequent Poster JustStandups's Avatar
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    Re: JS550 Fuel Issue

    https://www.watcon.com/fuel-system/c...uni-round-body

    Get a mikuni rebuild kit, and replace the fuel lines and primer if it has one. I would also bypass the fuel selector straight from the reserve line if you think its sucking air from there.

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  4. #4
    Frequent Poster sorejo's Avatar
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    Re: JS550 Fuel Issue

    I have heard that you sand the plastic cover to fit in there better. Does that help with the o-ring?
    1986 Kawasaki JS550

  5. #5
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: JS550 Fuel Issue

    Quote Originally Posted by sorejo View Post
    So I just picked up a '86 550 and am having issues starting it. I have poured gas directly into the carbs and it runs till it burns off the fuel I add.
    The 1986 has more starting problems than any other Jet Ski. But first place
    is closely followed by the 87', 88', and 89' JS550's.

    When the needle and seat doesn't open, the carb appears to have a fuel pump or
    a fuel supply problem. But it is not the problem.

    If the needle and seat isn't stuck, it is very likely that the needle and seat
    isn't opening because of a vacuum leak. Hopefully it has been rebuilt before,
    otherwise the list can be long.

    1) That carb has a defect in the pilot (starting) circuit.
    2) That carb (1986) tends to drain the contents of the float chamber into the engine.
    3) Vacuum leaks on the carb and float diaphragm.
    4) Vacuum leaks on all the intake gaskets (sometimes the cylinder base gasket).
    5) Vacuum and/or pressure leaks on the front main seal (very Common).

    6) The rings were out of service limit before the original owner purchased the new 550.
    7) Problems with the engine producing manifold vacuum because the piston rings
    are so worn out. Ring end gaps of 1/8" is common.

    Of course poking holes in the fuel filter didn't help.


    Is the stock rev limiter still in place? It is essential part in the starting process.


    Bill M.

    The good news is they can be fixed to be a reliable and fun jetski.

    But finding good parts is getting difficult.
    Last edited by wmazz; 11-25-2020 at 02:14 AM.
    Horsepower == Speed, RPM != Speed



  6. #6
    Frequent Poster sorejo's Avatar
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    Re: JS550 Fuel Issue

    A family friend used to own a Kawasaki jet ski dealership in the 80's and hopefully has some parts laying around. I think we are just going to swap the carbs for something else. I have a Westcoast side draft intake mani that I was considering using but I have read that they make a mess inside the hull... Do you recommend I use them or buy a different traditional intake mani?
    1986 Kawasaki JS550

  7. #7
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: JS550 Fuel Issue

    I think you should try to rebuild the stock carb first.

    There is a good chance that any carb you get a hold of, will have a stiff
    float diaphragm (including your stock carb), and it will need rebuilding.

    Most people would recommend a 44 sbn carb for your ski, I prefer the 38bn
    from an older 550, or any 440. I suppose a 38 sbn would work too, but I
    do not have jet specs.

    If you choose a different carb, you will need to purchase intake manifold spacers,
    or modify your stock throttle cable (for a 38bn). IMO it is not a good time to
    install a side draft manifold, before you get the engine starting and running
    reliably.

    It is possible that your carb has the old green colored gaskets, and they
    can be difficult to remove.

    If you choose to rebuild your stock carb, you may need to modify a 10mm
    socket to remove the needle and seat. It helps to have a flat surface
    to flat sand some parts (you can make one from a piece of glass), and
    if you want to repair the defect in the pilot circuit, you will need a .033"
    jet drill and a pin vise. I can help you find what you need.

    Cutting your own gaskets is an advantage, but there is decent (thick) carb
    base gaskets available.


    Bill M.

    When rebuilding BN carbs, it is important to use a pop-off tester. Also a
    new 1.5 n/s should be sufficient. I don't remember what was stock. But
    the larger the seat, the more important a pop-off tester is for a reliable
    rebuild.
    Last edited by wmazz; 11-25-2020 at 04:02 PM.
    Horsepower == Speed, RPM != Speed



  8. #8
    Frequent Poster sorejo's Avatar
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    Re: JS550 Fuel Issue

    It does have the green gaskets... is that original?
    1986 Kawasaki JS550

  9. #9
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: JS550 Fuel Issue

    Green gaskets are the thick aftermarket gaskets.
    Horsepower == Speed, RPM != Speed



  10. #10
    PWCToday.com Is My Home Away From Home MrSki's Avatar
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    Re: JS550 Fuel Issue

    If it were me, I'd rebuild the entire engine and toss the BN carb for a SBN. That way you know what you have and not chasing issue after issue on such an old boat. But that's just me.
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