system to the high-speed system. The acceleration system squirts a stream of fuel into the air horn when the fuel pedal is pressed and the throttle plates swing open. Without the acceleration system, too much fuel would rush into the engine, as the throttle quickly opened. The mixture would become too lean for combustion and the engine would STALL or HESITATE. The acceleration system prevents a lean air-fuel mixture from upsetting a smooth increase in engine speed.

The basic parts of the acceleration system are the pump linkage, the accelerator pump, the pump check ball, the pump reservoir, the pump check weight, and the pump nozzle.

The ACCELERATOR PUMP develops the pressure to force fuel out of the pump nozzle and into the air horn. There are two types of accelerator pumps - piston and diaphragm type (figs. 4-22 and 4-23).

Figure 4-22. - Piston accelerator pump.

Figure 4-23. - Diaphragm accelerator pump.