My 03 kx250 had smoked like a mesquito sprayer and ran a little sluggish. After reading so many posts about how the 03's are stock jetted really rich, I dropped the pilot and maine one size each and the result is amazing!! The smoke is gone and I can't shift gears without the front tire raisin' up....I love it !!!! But how do I know it's not too lean??? I mean it runs better than any bike I've ever had, but that don't mean sh*t if it locks up the first good, hard ride.