i have an 02 400ex and i jus bored it out .010 over the only way it will start now is if the valves are real lose. but when they are to 'spec' it just backfires and turns over like it wants to start. i'm running out of ideas and need a few suggestions ... thanks

 

i have an 04 400ex.and mines is a b!tch to start..try changin spark plug..carb my have something in it..or something clogged in the needle.think little **** before you freak out though lol..good luck