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Just picked up a 91 650SX. I got it for $400 with the disclosure that for some reason after 20mins of riding it starts to get hot. If you turn it off, it won't restart or struggles to restart till it cools for another 20mins. Its like a 20mins of riding and 20mins of cooling, so I was told. The ski 100% stock but the pipe I'm not sure. Its a raw metal pipe that looks aftermarket but it doesn't say anything. Therefore I'm wondering if its lean jetting but the plugs looks black brown. Is there areas of the cooling lines I should check and blow out or a pump I should replace. I'm new to skis as this is my first one. I want to dial it in as best I can before taking it to the lake to not add more wear and tear if I can do something about it now. Thanks so much
 

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Welcome to the forum! From what it sounds in your discription the carb has not been rejetted after changing from the factory exaust, this can cause a lean condition and get hot. It would be helpful if you post pictures of your exaust so it can be identified. Also check the crank seals and carb boot for leaks. I do this by spraying the seals and carb boot while the engine is idleing. If the RPMs change there is a leak. The leak needs to be fixed as soon as possible because a lean fuel mixture will kill the motor,
 

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A buddy came over and said the exhaust is stock so that shouldn't be a problem. We hooked it up to the hose and ran it for a good 15 mins. Then checked the spark plugs. Both plugs appeared to have a milky watery look on them, even though it ran good. We are both thinking the headgasket could be leaking. However who knows if this is headgasket is causeing it to run hot or it is just a side effect that occured from running hot from another cause. I'm going to pull the head cap off and see what it looks like.
 

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Welcome to the forum! From what it sounds in your discription the carb has not been rejetted after changing from the factory exaust, this can cause a lean condition and get hot. It would be helpful if you post pictures of your exaust so it can be identified. Also check the crank seals and carb boot for leaks. I do this by spraying the seals and carb boot while the engine is idleing. If the RPMs change there is a leak. The leak needs to be fixed as soon as possible because a lean fuel mixture will kill the motor,
Thank you for the welcome to the forum. I will try the spray technique but what is it that I spray on these seals. Is it carb/choke cleaner? I think I've heard I need to spray something that when it gets sucked in is flammable right? Sorry I'm kinda new to this. Thanks
 

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Thank you for the welcome to the forum. I will try the spray technique but what is it that I spray on these seals. Is it carb/choke cleaner? I think I've heard I need to spray something that when it gets sucked in is flammable right? Sorry I'm kinda new to this. Thanks
even with a stock pipe, def want to check the carb jetting.

Milky white spark plug...? Do you have a pic?
Here is a quick find on google on reading spark plugs. What does yours look like?

If you think you might have a gasket leak, you can use the old school spray technique... it will be sucked in by the vacuum cause by the gasket leak and the engine will rev. Use carb cleaner... use it sparingly.... out in the open... with a fire extinguisher close by...

remember some spray may get sucked in at the air filter by proximity.
 
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