Wont rev up
Hello everyone, this is my first time posting. I have an 02 Polaris Sportsman 400 four stroke 4x4. It wouldnt rev up and was back firing through the air box. This is what I have done to bike. First I replaced the cam and exhaust rocker and adjusted valves to spec. While relpacing cam noticed broken wire for the coolant temp sensor so I replaced that also. The Bike fired right up and runs great but wont rev up past 1/4 throttle. It bogs out like its not getting fuel. So I drained fuel tank, replaced the fuel filter, cleaned the carb and air filter and also rebuilt the fuel pump and new spark plug. Still no change. Took the fuel line from tank and plumbed it directly into carb and held the tank up so it would gravity feed, bypassing the fuel pump and still no change. Starts and runs fine but wont rev up past 1/4 throttle. Seems to run a lil better with air box top off but not like it should. Did a compression check and has lots of compression. I then replaced the stator and cdi box and swapped coils with a different bike. and still no change. I have called every polaris dealer in the area and have gotten no help. I have bypassed the reverse override switch buy unplugging the sensors at the trany. still no change. battery is good and has good voltage. I cant for the life of me figure it out. PLEASE SOMEONE HELP ME!! I have cleaned the carb and adjusted the needle and air screw and no change. have been through carb 100 times and still wont rev up past 1/4 throttle. seems to run a lil better when its cold but still revs up slow and (doggy). I have tried everything i can think on and cant figure it out. Someone please help me. THANK YOU!