I just stepped up to the four-stroke world and bought a used 07' YZ450. The bike seems to run well but it just needs some tuning. At first crack of the throttle it boggs but at the mid and top end it rips. When the air temp rises the bike runs great from low to top end. Im just wandering what i need to do to adjust the carb. I bought an after market air/fuel mixure screw thinking that would solve the problem but the problem did not improve.