I have a 03 polaris sportsman 700. What I have done to it is , plugs, head base gasket, ( engine specked out awesome inside)air filter,kokusan ignition,drive belt,complete carb rebuild with 1.57, screw set at 2 turns out. New needle jet and jet needle( clip in middle)This thing sat two years, heads plugs were carbon black inside. When I got it it would bog out at 1/2 throttle. Carb boot is good,fuel filter new. The problem now is it still Boggs out 1/2 throttle idles and runs low end find. Last night I noticed theme exhaust header was glowing?))) any ideas? I think I went through all the basic stuff on this thing....

 

Running lean if the exhaust pipes are red hot. Sounds like something stopped up in the carb or you need to go larger on the main jet if you're sure it's not an air leak.