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I have a 1999 Polaris Sportsman 500 ,Last summer I went on an ATV run of about a hundred miles, Towards the end of the ride I noticed the motor was starting to knock and it did not seem to have much power,especially upon acceleration. When I got the machine home I had the cam replaced which cured the knocking but when I test drove it at the shop the power still was not right...actually not any better than before the repair. I told the mechanic about it and he messed around with it for a few minutes and determined that the air box was not sealed properly and put a new gasket in. The problem seemed to be solved but since I got it home the problem has resurfaced. I tested the compression ,It's fine and,replaced the plug and fuel filter to no avail..The problem is not constant ,sometimes it runs great. What do you think is the problem ?????.


Thanks,

Randy
 

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Hey Im a certified polaris tech :) My guess would be that the engine is still blown up. Compression checks on 4 stroke engine usually dont tell you ****. You need to do a leak down test to the engine which will tell you if you are getting positive pressure to the crankshaft. The shop that worked on your bike should have done all this if they are reputable. My guess is that the rip in your carb adaptor let that 100 miles of dirt go for a nice ride in your engine. Wearing down the cylinder walls and rings. Its critical on small engines to frequent oil changes and have clean air intake systems.
 
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