I'll bet that Mogman hit the nail on the head, you have a plugged screen. Take off the side of the carb that has the large single screw in the center. you will see a small cavity (about 1/4 inch in diameter) with a very fine mesh screen in it. Carefully remove it with a sharp pin or equivalent and hold it in a tweezers or needle nose and burn off the fuz you see collected on it. Rinse off the debrie in clean fuel or alcohol and repace it back in the cavity and put the plate back on the carb.