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Discussion Starter #1 (Edited)
I picked up 2 js550's from 2 different people and they both have the same problem. Hopefully someone on here can point me in the right direction. They crank over very slowly. I put new batteries on them, checked all the connections, and checked the batteries and cables with a multimeter. Everything checks out fine. If I pull the spark plugs the engines will spin like crazy. The only way I can get them to start is to jump them off my truck batteries. Even then, they just barely spin fast enough. The previous owner of one of them said that he milled the head .035", but the other previous owner said he did not know about any mods. Could the increased compression cause this problem? If so, how do others overcome this issue. Any suggestions are appreciated.
 

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I picked up 2 js550's from 2 different people and they both have the same problem. Hopefully someone on here can point me in the right direction. They crank over very slowly. I put new batteries on them, checked all the connections, and checked the batteries and cables with a multimeter. Everything checks out fine. If I pull the spark plugs the engines will spin like crazy. The only way I can get them to start is to jump them off my truck batteries. Even then, they just barely spin fast enough. The previous owner of one of them said that he milled the head .035", but the other previous owner said he did not know about any mods. Could the increased compression cause this problem? If so, how do others overcome this issue. Any suggestions are appreciated.
Check the starter, and make sure the batteries are fully charged. Having it milled shouldn't matter
 

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I just bought a 1990 550SX that has the EXACT same problem. It turns over extremely slow with the plugs in but if I pull one of both plugs it turns over really fast. I'm using a truck battery right now til I get it running then I'll buy a smaller one when it's time to hit the lake.

I'm thinking outside the box here and wondering if a mouse or something nested in the exhaust pipe and clogged it now there's no where for the exhaust preasure to go. It spins freely and quickly with the plugs out.
 

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I have had my 91 js550 since 91 and I know exactly what you are talking about. I have only experienced this issue over the last few years. To be honest it is only an issue the first time I start it in the season or after it sits for a long period of time for me. I honestly think it has more to do with the impella then anything else. Removing the plugs just gets rid of all back pressure so the starter is just fighting the impeller now. When this first happened I replaced the starter immedietly and it was no different. My ritual now is to spin the motor without the plugs a few times and I spray the impella down with WD40. Once I do this I can get it to start even cranking slowly. As long as there are no long sits between uses I never have an issue again.
 

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I am experiencing the same problem also... I suspect it really has something to do with the types of starter motors they are selling these days. I noticed mine does not have the third mounting point to support the back end of the starter against the crankcase. With out that support the torque required to start the engine forces the armature to work against the bushings.... wearing it out prematurely.
 

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Find stock starter and rebuild it. Very interesting what webvation was talkin bout. To avoid that id spray her down with wd40 when you winterize it. And grease it regularly.
 

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New to the forum, but having the same problems with my '88 JS550. It was actually running great, then it was my son's turn on it, and after rolling it over, it would turn over very slowly. I put on a new battery, same thing. New starter, same thing. When I pull the plugs, it turns over very quickly. I have a starter selenoid on order and will try it, but I doubt that's it, because I bypassed it by arcing the two posts to each other with the same slow turn over. Any suggestions? Thanks!
 
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