hey guys,my 2000 sportsmam 500is still acting up.I was snowplowing one day & started losing power.I've changed the plug,(I have good spark),Ive pulled the carb.,(it was clean with no obstructions),ther is no restriction in the air box,everything in the manual leads me to believe the "speed limiting switch" is causing this problem,but it tests o.k. She starts up & idles fine,but bucks & spits at 1/4 throttle,& barely has enough power to move her across the garage. I haven't checked timing yet,but when it started losing power,I was convinced I only had a fouled plug. Any ideas?  

it does sound like the timing is off.

however it could be the speed limiting switch,and it not test badly until the problem occurs.

my suggestion is ride it until it starts losing power and then test the switch. (if you haven't done this already)  

I finally got to the bottem of the problem here. The cam shaft is shot!! The exhaust lobe is gone.Is this acommon issue with these machines?