I have an 04 Yamaha Yz250f. The elevation is about 5,280 ft (a mile high) and my bike has a Yoshimura Trc Comp Series Slip-On Exhaustwith the spark arrestor removed. The rest of the motor is stock. I'm currently running a Keihin 168 Main Jet and it seems to run well if not a little bit rich. I was just curious what other people have to say about it.