its normal to hesistate slightly after idling for a long period of time, its caused by the engine "loading up"
the fuel flows into the carb and down to the bottom of the crankcase, where it waits for the piston to move down and force the fuel up through the ports in the sleeve, if the engine is running at a lower rpm it isnt burning as much fuel, hence the extra will "load up" in the bottom of the crankcase, when you add throttle your feeding more air, more fuel from the tank, and pulling the fuel sitting in the bottom of the crankcase in at once hence it bogs a bit, then when you let off and punch the throttle to max again its fine.

Lean the low speed about 1/16th of a turn and go fly.