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  1. #1

    TWO 2005 Kawasaki STX-15F's runs like crap

    Guys and Gals,

    I have searched for similar threads and I cant find anything.

    One of my friends has two STX-15F's. They both sat idle for almost two years.
    I have completely drained the fuel system all the way to the injectors,
    Refilled with fresh 93,
    tested the fuel pumps,
    Checked the oil,
    compression is good,
    water flow is good,
    Replaced the batteries,
    and they still run like crap.

    I have not changed the spark plugs which I know are at least two-four years old.

    I will go get new plugs and try them ASAP but here are the symptoms and I want to know if any of you have seen this before. Its strange since both are doing the exact same thing.

    We took them today to the river after getting them both to fire up on the trailer. Both of them fired up but if you held the throttle at a steady position the RPM would bounce around erratically. They would not achieve max RPM and would die suddenly some times. There was no power and one of them wouldn't even idle well. Every once in a while I could hit full throttle and there was almost full power for a second or so. Sometimes I would hit the throttle all the way and there would be little to no increase in engine RPM. The weird thing is that neither jet ski would show the speed of the bike in MPH and neither would show any Check Engine Light (CEL). They both just showed 0 MPH. Both skis have almost exactly 100 easy hours on them.

    Any Ideas?

    Best Regards,

  2. #2
    Change the plugs for sure. They should be changed every 100 hours anyway. Why are you putting 93 octane in these boats? If they are stock you only need a good 87 octane. They will run better on the octane they are designed for anyway. If these boats were last ridden in salt water and not rinsed down good you could have a wire corroded somewhere . . .

    I know this is not what you /your friend want to hear, but do not let these things sit for two years and not be started! OK. change those plugs and i bet those 15's are happy again..

  3. #3
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
    Join Date
    May 2008
    Check the silicone connector that goes between the header and the waterbox, it should be blue in color. If this hose has any holes in it exhaust will suffocate the engine and they will run like crap. You said the displays do not show the speed, do they show anything? Is there any water in the display? drops or haze? I couldnt explain why but these machines tend to freak out if the lcd display gets water in it. If the displays arent wet check to see if the paddle wheel is corroded and bound up. Post back when you have changed the plugs and checked for holes in the coupler.


  4. #4
    Thanks guys,

    I have a set also, we start them every two weeks at least. My friend is not so mechanically inclined.

    We are going to start with the plugs and fuel filters. There is no condensation in either of the gauges. They both show everything well except for any forward movement. I didnít think to check the paddle wheel when we were on the water but I bet they are both hung up. They have never ever seen salt water.

    I didnít know they needed 87 octane. They are bone stock. I just assumed they needed 93.

    Best Regards,

  5. #5
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
    Join Date
    May 2008
    using 93 will not damage anything but it has a small amount less energy than 87 does but it is also more forgiving when run in hot conditions or under high compression. Seriously though check the exhaust coupler too, its easy to do but could be your problem.


  6. #6
    Thanks for the replies guys!

    It was the plugs. We changed them on both skis and they run like a top. Thanks for all the help. My buddy is happy as hell.

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