I have a kx 125 it idles fine but when i am driving it it wont rev out

Clean the carb. Some trash is partially blocking the main jet.

change the plug then drain the carb and ck compression and that will tell u the story

check the carb float and the float settings. also clean all the jets out. check the joke aint sticking. check the condition of the air filter for rips or holes as that would explain why the bike is bogging when reved

first drain the carby, then set your air mixture screw 2 turns out, from the fully turned in position. The starting proceedure is as follows, when the engine is COLD, turn on fuel, pull on the choke fully, and kick the engine over. DO NOT use any throttle, when the engine is cold, and the choke is on. Remember Choke on, NO throttle.
When warm, no choke, and a little throttle when kicking.

sounds like you need to rejet the carb..

some things to try,
adjust the idle using the black knob on the carb,
check air filter is clean,
remove and clean carb

Service your carb.I think you will find your pilot jet is blocked.

Remove the slide from the throat of the carb, move the clip on the jet needle one notch lower. This will richen the low end fuel/air mix. - - - Simple, quick, and free.

Do it, then rate this answer as "Very Helpful". Thanks.

sounds like your idle jet is clogged, remove your carb and clean idle jet cause it won't idle or kick start without it...good luck to you friend...Tim