I have a 99 Polaris Sportsman 500 that I recently replaced the piston and rings on (Wisco oversized). After the replacement it's extremely hard to start. When pull starting it's physically difficult to get the piston to turn over. Have to tug/bounce on pull cord to get piston to turn over. If the spark plug is removed I can pull it over without issue. I have other symptoms that I believe are related to this root cause - such as it bogging out at 1/3 throttle, sensitive carb idle (once warmed up will kill - if idle adjusted won't start). And the plug is new and you can see an image attached.

Any know what I can look for? Seems like there is too much compression or the timing is off - even thought the TDC marks were used for piston installation according to the Service Manual.

Thanks

 

Check the cam exhaust detent spring and arm on the left side of the cam. If its set wrong or spring not correctly in place will cause hard starting,rich condition and and bogging down.

 

old polaris tech -

Thanks for the reply, greatly appreciate. I'm looking up the "cam exhaust detent spring and arm" in the service manual now and will review.

Would these symptoms still exist when the spark plug is removed if it is due to the "cam exhaust detent spring?"

 

This is the spring you're referring to... interesting. I can understand how this could have not been reinstalled correctly. I would have never looked there.

 

The spring could get out of place which its purpose is to bring the detent lever back against the stop after the engine cranks. This could have something to do with hard engine turnover and even recoil hard to pull..I KNOW,I've done this and experienced some of the symptoms you are having,hard start/recoil problem and wont throttle up.This may or not be your problem,but check that detent spring is wound properly and lever flips back with your finger. With the spark plug out it would be easier to turn over. Just a thought?? OPT