2003 KX 125: 1999 kx idles but dies when you rev it its like yo...

How did you get on with FTjoes fix? That would be my first thing to do, dont forget to take out the jets and give them a blow through, then treat the bike to a new plug if you haven't already. :)

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

Sounds like there could be a problem with the main jet not delivering sufficient fuel for normal running. Clean out the carb and check the jets and passages for obstructions and dirt.

Hello you have a
1. fuel starvation problem clogged carburetor jets.(clean the carb)
2. Intake leak carb joint/intake manifold.( start your motor get it to idle best you can spray wd40 around the carb joint if the rpms change you have a leak replace the carb joint or gasket/o-ring as needed.
3. crankshaft main seal magneto side leaking or worn main bearing.
check end play on the magneto side remove the cover plate firmly grab the end of the shaft with up an down motion if you can feel it move replace the main bearings and seals.
These are problem that will cause your motor to run lean and hesitate.
Hope this helps you with your problem

cable is bound up and carb slide is sticking. Remove and clean

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

try nexted hottest plug for ex. i had a b8eg standard and went to b7eg

Sounds like your mixture is to rich, let the bike idle, then unscrew your air mixture screw until the bike speeds up a little, then turn down the idle screw to the proper idle speed. If this doesn't help, has the motor been rebuilt recently. If so, they might have put a bigger jet in the carburator to make it run richer for a warranty on the motor. this lubricates the motor, less likely to freeze up from long high rpms. these can be replaced for a couple of dollars if that is the case.

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