going through the same problems with my new to me 99 sportsman, I traded my running 90 trail boss 4x4 for a none running sportsman. Replaced a bunch of stuff and it fired right up idled perfect but when I gave it gas it back fired through the carb and had no power. so today I took the rocker cover and rockers off to see the crank and found that the exhaust lobe wasn`t in good shape, I called polaris and $400 later a new cam and exhause rocker is on its way.

im haveing same problem but still no clue how to fix it is there anyone who can help me

Check the post above yours! Bad year for cam wear on exhaust lobes. They would idle great,but would pop back through carb and air box when giving throttle. Remove valve cover and check if exhaust lobe worn down on cam. May be your problem. If it is, order the exhaust rocker arm also as it usually gets grooved too! OPT

Hello forum, new here.

I followed the directions in this post and replaced my cam shaft then buttoned things back up according to the book.
Now the engine starts up, thruttles up, idles well and no more backfiring through the carb but when I took it for test drive the engine cutted off in about 50 yards while in motion. I was able to restart the engine but only to find it repeat the same symptoms in about 50 yard. Both time when the engine died it also locked both rear wheels as it skidded to a stop, at first I thought the engine ceased but I was able to restart it.

Any thought on what could cause this problem or what I did wrong?

Note:
I reviewed and rechecked each step of my endeavor, the only mistake I could have made maybe in the cam sprocket and timing chain relations. I didnt mark it well before the removal and I think it could be off by one tooth, would this cause the problem?

If the wheels are locking up it may not be the engine.. What model do you have?

its a 02 Sportman 500 HO.
Both times the engine quit and wheels locked and i skid to a stop.

Just crank it up and see if it will stay running in neutral. If it doesn't then you'll have to trace down the problem. Either a mechanical problem,piston seizing,etc or possibly could be loosing spark.. If it stays running,then could be a problem with clutches or gear case.

Thanks for the input.
I tried it in neutral, it revs up just fine and stay in idel when I return the throttle.

I didnt touch the clutches or gear case, could it go out just like that? this one has me puzzled.

Best way to tell is to pull the clutch cover and start from there with the clutches. Watch the operation of the clutches and belt.Put it in gear and drive it and see what it does.

Today was the first day that is warm enough for me want to touch the tools.
As I suspected, it was the timing. The sprocket was off (retard) by one key.
I can see why the engine would stall at higher RPM but not sure about the logic with locking up the rear wheels...weird.
Nonetheless, it's fixed. Thanks for all your input old tech...