Accelerator Pump: Description and Operation

Accelerator Pump:

The accelerator pump system is a positive displacement, piston type. It consists of a piston assembly that is activated by throttle movement through an overtravel spring.
The pump cavity fills from the top and the floating cup acts as an inlet check valve.
As the throttle is opened, and the pump piston is driven downward, pressure developed in the cavity seals the cup against the pump cavity well, causing the fuel to flow. An anti-siphon check ball and weight, located in the up channel are unseated and fuel is delivered through the pump discharge nozzles to the venturis. When the fuel supply in the pump channel is exhausted, the check ball and weight return to the seated position to prevent siphoning during high speed operation. When the throttle returns to the idle position, the return spring forces the piston upward and allows the pump cavity to refill.
The temperature compensation provision includes a bimetal restrictor valve located in bottom of the fuel bowl. Fuel is diverted through the restrictor back to the fuel bowl when fuel bowl temperature reaches a predetermined level. This will help prevent "slugging" from an over rich pump shot.