Problem with 250EX

[250rAL]

I'm hoping someone can give me an idea which way to go in diagnosing a problem with my son's 2003 250EX. When you try to accelerate in the midrange, about half throttle, it stumbles. It does fine below that and if you can get above that it will go full speed. The machine doesn't have very many hours on it and is completely stock. So far, I've replaced the plug and cleaned the carb(blew out the jets). The valves were adjusted about a year ago. The filter is clean. I was going to go richer on the needle but came to find that it was at the bottom notch already(stock apparently). I tried one leaner but it was the same. Since it's only in the midrange, I find it hard to believe it's not a carb problem. Can something electrical only affect the midrange like that?

[okieRrider]

I had this happen on my 400ex a few weeks ago. Try taking the airbox lid off and see if that helps out any. If it does it is running rich. Mine has a cam, kn filter, and slip on exhaust and thought i had it jetted right, running with the lid off. I put the lid back on and thats when she started boggin in the midrange.

[250rAL]

That's something to try but remember, it's completely stock and nothing has changed from when it was running right.