mitch a good way to check the low end would be to,and I'm sure you have seen people do this is to place your planes elevator or plane stand in front of the elevators then once its been brought to a good warm up on the engine,nail the throttle and the plane should not stumble nor dye immediately.it should transition smoothly.bring the low end in 2 clicks at a time until you reach the point you need.also if you havent already inspect the fuel line to carb insuring thats theres no air bubbles and the nipple to the carb (fitting) is tight.
good luck and happy flying!