My buddy has a 02 400ex and every time he guns it ,it bogs.He's cleaned out the carb already and the plug. The bike also smokes alot with a white smoke.Thanks for help.

 

When in about 2nd or 3rd gear just "creep up" on the gas......If the machine begins to break up prematurely,(before you would normally shift), you probably need a valve job or need to clean out the air filter....try these...and please get back....