Hey guys, I have a Polaris sportsman 500 and I have had it since 2001 maybe. Last September it started to have a loss of power. It would have half power at half throttle and if you went any further at full throttle then it felt like it was bogging down or half throttle. My dad had a guy work on it then he didn't know what was wrong with it and we brought it to a dealership. My dad put $1000+ in it and still didn't have it fixed. I got it back home, in pieces(really crappy service), and started to put it back together and put a new sparkplug in it and it ran like new. I got brand new itp mud lite xl tires on the front and regular mudlite on the back and a superwinch lt 3000lb and it has started doing it again. It has new royalpurple motor oil in it. I have never replaced the air filter cause my dad said it didn't need one, I have covered food plots in really sandy south Ga. where it was dusty. I have been searching on google and found something about the cam and flatspots. When it was worked on the guy had a supposedly "great" mechanic look at it and said it was fine. The only thing I have done to it before is change all the fluids and new tires, starter( going on 2nd one), and a belt. And thanks for helping me diagnose the speedometer problem also. Any help is appreciated.