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I'm trying to put together my old 89 650SX jet ski that has been out of service for 8 years. I've got it all repaired and put back together (It took a few tries since I took it apart in '01!). It now starts but as soon as it does the engine races and runs away. The kill switch would not even stop it. Luckily I had a rag ready that I stuffed in the carb to kill the air flow. I have not touched the intake or carb during the repair and everything is tight. I had the exhaust apart and the electricals that burnt up last time. I'm thinking it is an air leak somewhere but don't see anything obvious. Anyone have any ideas where to start? I'm trying to get it going for our holiday weekend lake trip. Thanks!!
 

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If the kill switch doesn't even stop it, then that points to a problem there in the electrical. Did you adjust your idle screw at all? I'm curious with all the work done if it did not get adjusted to where your idle revs all the way?
 

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Dont rev your jet ski out of the water. If there is a hot spot in the cylinder it will run like a diesel and rev till it blows. Pulling the spark plug caps wont stop it, as you found out you have to kill the air supply.
 

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I had that happen to me once with my wifes ski. It was when I first fired it up after winter. I didn't have the spark arrester removed so the rag wasn't an option for me. I was panicing thinking about the repair bill I was going to have if I couldn't shut it down. I finally hit the thumb throttle wondering if that was maybe stuck and that stopped it from running away. After I realized that it was dieseling because the kill switch didn't do anything.

I have never had that problem before and it has never happened since. Give it a try, but have the rag handy just in case.

Have you tried to restart it since, if so did it happen every time?
 

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either like they said u have an electrical problem. or your crankcase water drain is leaking air into the crankcase/primary compression chamber. lean engines like to run away because a lean mixture burns nice and hot and doesnt neccesarily need spark to ignite it. having ngk plugs dont help either because ngk's are commonly hot burning plugs which are great for 2strokes to burn the oil. but with a lean mixture case they can act like glowplugs. a kill switch will not kill a lean mixture runaway. my advice to u is remove the crankcase drain assembly and get a blockoff plate. fairly cheap and can be done with the engine still in the ski and its not a bad thing to do even if that is not the cause.

ive had the same thing happen to me once and im told that it is a common problem with kawi 650s
 
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