When jetting you should start with the main circuit with plug chop at WOT. When that's right, then do plug chop at half throttle to check clip position. Always start rich, then work towards lean, as rich will not hurt the engine, only performance. You should maybe start with a 160 main. If still to lean, go higher. Make sure you do plug chops correctly, closely following instructions on KDX site. Plug should look med. brown on insulator bottom (down inside). Do not run the bike lean, as it WILL cause damage. Every second counts! Hope this helps & good luck. P.S.- Make sure the fuel level (float height) is correct, as low level will cause lean condition. :D