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Thread: STX 900

  1. #1

    STX 900

    I'm working on a friends ski.

    Its a 2006 stx900. The previous owner blocked off the oil pump and removed the oil tank.

    I was under the impression that you should not do this to a kawasaki. I know its a bad idea on an ultra 150.

    The reason we are working on it is the middle cylinder has lost most of the compression. I've pulled the head cover and the cylinder walls are very smooth. The middle piston has a small chip in one side which is where I assume it lost compression.

    I've cycled the pistons up and down with the head cover off and everything looks like its working properly.

    Long story short, we took it to a local mechanic to see about the middle piston and they told him that everything is shot in his motor and he needs a new one. All the accessories are shot and have to be replaced. And that it shouldn't be run on premix, it needs to use the oil pump.

    I don't trust this assessment as the ski will run and move under its own power. It just wont always get up to speed. Sometime he would do a 360 and the motor will cut off.

    Completely shot motor just does not carry water to me.

    Any help or opinions are appreciated as always


  2. #2
    steve45's Avatar
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    Find a real mechanic!

    The Ultra 150 should not be run on pre-mix because it has balance shaft bearings that require oil from the pump. Not so with the 750, 900, and 1100 engines. I prefer oil injection, but pre-mix if fine on those.

    If the cylinders are smooth without any significant scoring (you can't feel anything with your finger nail), then you can probably hone them and install new pistons and rings.

    I'd recommend going through the carbs, splitting the case and replacing the crank seals, install a new starter, and replace the driveshaft bearing/holder.

  3. #3
    the other thing i noticed was that the gap had been pushed closed on the middle spark plug

  4. #4
    steve45's Avatar
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    Quote Originally Posted by ilts View Post
    the other thing i noticed was that the gap had been pushed closed on the middle spark plug
    Minor detail... At the very least, you'll have to pull the cylinders and look at the damage. New pistons/rings for sure, possibly honing/boring the cylinders. It would be a very good idea to inspect the crankcase and crankshaft for debris. Ideally, this should be done after splitting the case.

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