I have a 2002 400 Sportsman. It runs alright at idle but when I hit the throttle it runs really rough like the timing is retarded. I changed the air filter, fuel filter and spark plug. I had the carb apart and cleaned. Still the same problem. Is it possible that the ecm is out and if so is there a way to check it? Does anyone else have any ideas

 

Try setting the valves(.006) on both