That's exactly the same I had with my Poulan 25cc. I setup the engine for nice transition and good idle with clean top end. If I let it idle for minute or so then it hesitates when I open the throttle fast. Sometimes it just dies. Kind of like a lean low end on glow engine.
I figured that it is a glow plug getting to cold . When I kept glow plug powered on idle the engine could idle "the whole day" and be responsive to the throttle any time.