I had a Dr 750. I blow up the motor, I put an DR 800 in it. I cant get the 800 to run. Starts no problems. it looses power,and will not put through the gears smoothly .Have checked the cdi, and coils, the fuel is ok. It will not run with an air filter. the only thing thats different is a 2inch header pipe. can any one help me. thanks