1990 Kawasaki 550SX Piston Port motor idle speed and Mikuni 38mm carb
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  1. #1
    PWCToday.com Is My Home Away From Home Cliff's Avatar
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    1990 Kawasaki 550SX Piston Port motor idle speed and Mikuni 38mm carb

    Hi Guys,

    I have a question about the idle speed and about the stock Mikuni 38mm carb on my ski mentioned above. The ski is all stock. No motor mods or bolt one. I've owned this ski for one year and am new to stand ups. I have ridden/worked on my 'Doos since 1996.

    Here are my questions:

    1.) I have read that the idle should be at 1,100 rpms on the 550SX. Is that in or out of the water? (I'm assuming it's out of the water)

    2.) As for the Mikuni round body 38mm carb. Is it beneficial to upgrade to a 44mm carb with a stock motor?

    Other info...

    - the ski starts, idles and accelerates fine. But after I fall into the water and the kill switch lanyard has been pulled off and I try to restart it in the water. The motor doesn't restart. It only cranks. Once I finally get back to the beach and put it on the water stand and let it rest for awhile. That's when it starts right up without any problems.

    Could this be because of:

    1.) leaky needle/seat
    2.) carb needs better fine tuning
    3.) temperamental carb to begin with
    4.) ???

    I don't know the history of this ski. My compression test shows 148/150 psi. But that doesn't tell me anything about the crank or the crank seals. I only know that the previous owner said that the top was rebuilt and 10 hours has been put on the motor. I don't know if the bottom end has ever been rebuilt or not.

    Has a quick steer plate, trigger throttle, extended ride plate, ODI Lock On grips, Jet Trim mat, Stainless 15.5 impeller and fresh paint.

    Thank You for any/all input!


    Cliff


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  2. #2
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    Re: 1990 Kawasaki 550SX Piston Port motor idle speed and Mikuni 38mm carb

    1--That's in the water
    2--Stepping up to a 44mm carb on a stock motor will only help you burn more fuel.

    2.5----Carb probably needs a kit due to age and then dialed in.
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  3. #3
    PWCToday.com Is My Home Away From Home Cliff's Avatar
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    Re: 1990 Kawasaki 550SX Piston Port motor idle speed and Mikuni 38mm carb

    Thank You for the info!

    That helps me a great deal!


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  4. #4
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    Re: 1990 Kawasaki 550SX Piston Port motor idle speed and Mikuni 38mm carb

    bn44 is the stock carb on a 90sx piston port.

  5. #5
    PWCToday.com Is My Home Away From Home Cliff's Avatar
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    Re: 1990 Kawasaki 550SX Piston Port motor idle speed and Mikuni 38mm carb

    So the stock carb is a BN44 and not a 38mm(I assume it's also a BN & not an SBN)?

    I think it's called a round body carb and the gaskets are what looks like cork held with Allen head screws.


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  6. #6
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    Re: 1990 Kawasaki 550SX Piston Port motor idle speed and Mikuni 38mm carb

    Quote Originally Posted by Cliff View Post
    So the stock carb is a BN44 and not a 38mm(I assume it's also a BN & not an SBN)?

    I think it's called a round body carb and the gaskets are what looks like cork held with Allen head screws.


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    Stock should be a bn44 for the 86-90 The 91 and up reed engine came with a keihn 38 though.

    I have the 44 on my 90 mine will fire up out of water easily and in the water when cold i gotta hit the primer 2-3 times its good.Once warm and sits for a minute it may take 3-4 seconds cranking with 1/4 throttle and if its bad will have to hold wide open then back off once it begins to fire.They basically flood once warm is what i hear.I have a new needle and seat to install but havent got to it yet.

    My old 86 was about the same just a tad easier to fire usually never needed full throttle most times just a touch.

  7. #7
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    Re: 1990 Kawasaki 550SX Piston Port motor idle speed and Mikuni 38mm carb

    I just rebuilt my 90' 550 piston port 550sx. I put the stock 44BN carb back on as well. You will read a lot about how most ppl hate his carb and that its a bi*&$ to tune but there not impossible. Your issue sounds like the seat leaks fuel to the the main venturi after you fall thus flooding the engine and causing hard starting while warm, common issue with this carb.

    This directly relates to pop off pressure, you need to check that your needle & seat doesn't leak and has a good seal first. This can be done by doing a pop off pressure test. There's a good doc some where on this form explaining the details about tuning the carb, it was taken out of a 90's ski mag...
    The other issue with this carb is that it requires a ridiculous low pop off pressure to run right and the lower that pressure is will tend to cause the problem you are explaining.

  8. #8
    PWCToday.com Is My Home Away From Home Cliff's Avatar
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    Re: 1990 Kawasaki 550SX Piston Port motor idle speed and Mikuni 38mm carb

    Great info, Chip!

    Thank You!

    I have the Mikuni rebuild kit and was thinking that the carb would need a look to see where it's at since I don't know the entire history of this ski.

    I will do a pop off test and see how it goes from there.

    I will search out this document you speak of and read it.

    What would be this "low pop off pressure" range be?


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  9. #9
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    Re: 1990 Kawasaki 550SX Piston Port motor idle speed and Mikuni 38mm carb

    I have a new needle and seat for mine as well just havent installed it but from engine experience its like what was described more like a flooding issue symptoms.

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