Accelerator Pump: Description and Operation

Fig. 28 Temperature compensated accelerated pump. Motorcraft model 2150A carburetor:

The temperature compensated accelerator pump, Fig. 28, is used on vehicles equipped with the Motorcraft 2150A model carburetor, allows delivery of a large pump capacity to facilitate cold engine requirements and a smaller pump capacity during warm engine operation.

The amount of fuel delivered during warm engine operation is a function of the rate at which the accelerator pedal is applied (fast application/low capacity, slow application/high capacity).
- The design incorporates a bypass bleed controlled by a vacuum operated valve.
- Normally, the input signal controlling the valve position is manifold vacuum switched by a PVS located in the engine coolant system.
- The valve is normally closed when no vacuum is applied, allowing full pump capacity during cold operation.
- With vacuum applied, the pump functions as a rate sensitive valve controlling the amount of fuel bypassed back to the carburetor fuel bowl and not delivered to the intake manifold air stream.