throttle stumble

[Dusty]

I am having a annoying problem with carb on my nieces 250ex. Stabbing on the throttle from low rpms causes the engine to stumble, even die. If this where just a problem from idle, I could live with it. When riding, and getting off then on the throttle sometimes causes the same. The bike is stock, stock jetting and airfilter. I have tried removing the airbox lid, and even the muffler endcap thinking it was restricted and loading up. I have also lowered the needle to the top clip (it was set to the bottom), still no change. Any one got any suggestions? Am I going the wrong way?

Thanx,
Brian

[Dusty]

Nobody's experienced this? I'm not that experienced with jetting, but it appears to be in the needle jet circuit. Like I said in my first post, the clip was on the bottom to start and hasn't made a difference raising it to the top. There are only three on the stock needle. The bike runs fine in any of these positions, so I'm kind of stumped as to whether its lean, or fat. Any suggestions would be appreciated.
Thanx,
Brian