I recently purchased a 2003 CR 250. When i test rode it i was mostly in power band. I got it out in the hills and noticed a low end bog. It runs beautiful in the top end but right before power band kicks in if i hit the brake and punch it it bogs. Ive adjusted the ring on my needle. Ive changed spark plugs. it came with a 390 main jet and i tried a 420. it was worse. the guy i bought it off says it ran awesome before he parked it. If anyone has any suggestions or help please let me know.