Recently my -02 yz250f started dying when i snap the throttle, in gear or in neutral.
If i let go of the throttle it cames back to life.
No popping.
If i turn the trottle real slow the first 1/8 its ok up to W.O.

I tryed the airskrew in several positions, lovered/raised the needle clip, cleaned the acc-pumpdiaphragm.
Bike was kinda O.K. at first then slowly became like this. Normally runs 100 octane, now tried VP ms103 with same results except at full throttle when it flyes!!
Have to check the diaphragm again to make sure it is ok.
HELP!

It is your accelerator pump. These bikes are notorious for this and it is not your jetting. Check out posts on the "BK MOD".

It shortens your acceleration spray duration and will fix the bottom end bog. You may have to richen up the jetting once this is done. There area million posts here on how to do it. Check out Garrett's website off the main page. Good detail there on how to do this mod.

Good luck!

If this is happening when you just start it maybe it's just because it's cold.

Sounds like its time to clean the Carb & jets. Clean your idle/pilot jet.
Sounds like its clogged/plugged.

yeh clean the pilot air jet.