i ride a 2003 kfx 400 just put on a K&N filter took off the air box lid and put in 142 main jet. now the power is kind of sluggish feeling and the power falls of on the top end. does any one know whether it would be to lean or to rich. could anyone else who has ever done these mods tell me what size main jet they used. I ride about 1000-1500 feet elevation. also, would taking the end cap of your exhaust improve the power at all. or would it just make the quad louder. I definatly dont want it too loud. that is annoying. I just want a leetle bit more power. any help would be appriciated. Thanks.

 

sounds lean, fatten it up a bit and see if it gets better or worse. also, look at you spark plug, if its a blackish or dark dark color its rich, if its a light tan or white its lean, optimum is a cardboard brown.