could be lots of stuff,make sure your fuel line is on the correct carb nipple. take the carb off and make sure the pulse hole is clear and that the gasket isnt covering it . is the carb clean ?any leaks in the lower half of the engine will not allow suction for the pulse to pull fuel to the carb . carefully remove the steel diaphram cover , remove and inspect the rubber diaphram look for holes , replace as neccesary. pull needles from carb while it is off and dissasembled spray carb cleaner thru needles and clean needles let dry , re assemble