Hello guys! Last weekend my buddy put a new top end in my '08 KTM 300 XC. Next day we went out for a ride. Bike started on 1st or 2nd kick, had a good compression, but on high rpm interupted. I replaced the spark plug and had the same results, I've checked the power valve/timing and it was okay. I've noticed that when I removed the air filter, bike ran better. What do you guys think? What else I should check? Thank you.