When the engine does not accelerate properly, check the accelerating pump circuit for dirt. If the pump inlet check valve (25) does not seat, fuel will return to the float bowl instead of discharging through the pump discharge passages (26). This can be checked by removing the main body cover and operating the pump with a small amount of fuel in the bowl. If the check ball is leaking, air or fuel will bubble back into the float bowl through the inlet hole. After cleaning this seat extreme care should be taken when reinstalling the pump piston to be sure the piston leather is not damaged and that it contacts the cylinder wall. If the leather is not a snug fit against the cylinder wall, fuel will leak by the piston on acceleration, causing a weak discharge.

To clean the accelerating pump system, remove piston assembly and check ball retainer and check ball from bottom of cylinder. Remove pump discharge needle valve (28). All channels can then be cleaned of all foreign matter by blowing out with compress air. The small holes or restrictions in the discharge nozzle should be checked and when working properly should deliver a fine, solid and round steam. When the system is in good condition, a quick steady stream will flow from the discharge outlet the instant the throttle is opened.