I recently bought a 2005 YZ 450f it had about 6 hrs. on it but had been sitting all that time with gas in the carb. After cleaning the carb countless times with no great sucess, I replaced all the jets and float. The bike starts and runs very strong but makes a lot of engine noise, has a bad vibration and back-fires. Also, the header pipe right out of the engine gets extremely hot 15-20 seconds after starting. I drained all the oil and checked the filter. The oil was brand new without a trace of metal. I pulled the side cover and clutch off... it looks like it had never been started. I also checked the valve clearance and that was fine. WHAT THE HELL IS WRONG WITH THIS BIKE!!! Can someone help?