There is an old walbro with an accererator pump on the side that pumps when the vacuum drops on acceleration. Fuel cavity on the side with a diaphram spring loaded in one direction and held back with high vacuum. Throttle opens, vacuum drops, fuel squirts in. Sounds strange idling in complete two stroke smooth. Dousn't hesitate when you crank the throttle open. Landing aproach sounds the same, smooth 2 stroking all the way in.