The accelerating pump is connected to the throttle shaft by means of link (33) and operating lever (32). The function of the accelerating assembly is to temporarily enrich the mixture for rapid acceleration. The fuel is drawn into the pump chamber (29) through pump inlet check valve (25) on the upward stroke of pump piston (30) when closing the throttle. When the throttle is opened, the pump piston (30) moves downward, closing the pump check valve (25) and forcing the displaced fuel through passage (24) to overcome the weight of the pump discharge valve needle (28). The accelerating fuel then goes around the valve needle and out the pump discharge nozzle (26).

A slot in the pump piston stem allows the pump operating rod (31) to overrun the pump piston (30) when the throttle is opened suddenly. This overrun causes the pump piston to be subjected to the pressure of the spring (27), thereby giving a prolonged discharge of the accelerating fuel.

The accelerating pump is provided with an adjustment for varying the quantity of the accelerating charge. This adjustment is made by changing the position of the pump link (33) in the holes of the operating lever (32). The position farthest away from the pivot point is the cold weather setting since it gives the greatest discharge. The middle position is the average setting, and the position nearest the pivot is used under conditions of very hot weather.