First remove the air box lid, and leave it off, this will increase airflow. Next, replace the head gasket with one from an 86 ATC 250r or CR250r. This will increase the compression ratio. buy an aftermarket pipe and silencer like FMF fatty pipe and turbine core silencer. You will need to re-jet your carb ( you can have a good bike mechanic do this if your not comfortable doing it yourself ) and give the bike a good tune up. It probably wouldn't hurt to have it bored out and new piston and rings installed too, if you can afford it. You can do more to the engine ( port and polish etc.) but it starts to get expensive. Well anyways I hope this helps.
