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Discussion Starter #1 (Edited)
I bought a ski-doo mach 1 1990 with a 1993 mxz rotax 470 engine.
I rode it for 3 days and the engine stops without any reason in a trail. I check my compression and i found the left cylinder to be defective my compressions were only 65 and the right cylinder was 165. My piston and my rings were burned.
I sended my engine to a friend of mine who rebuilt engine and it was running fine again compressions were the same on each side
and the engine was going well but after 30 miles the engine stops again and the same problem came back i have to replace the piston and rings again and i have to bore the cylinder.
All the gaskets were replace and the crank was like new is it because i have a defective carburator on my left cylinder does the mixture was to lean. Youre help will be appreciate.
I added the pictures of my piston
 

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Thats a lean burn down and it's probably an air leak, check your rubber boot that connects the carb to cylinder for cracks. Carb would not be defective, it would or could be a plugged jet also. shane
 

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Discussion Starter #3
Thank you! after a close inspection there is a crack under the boot
It was exactly what you told me thank you shane for your help
 

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bad crankseal would cause leanburn too.
 
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