PRINCIPLES GASOLINE/DIESEL FUEL SYSTEMS - OD1620
- LESSON 1/TASK 2
FIGURE 19. MECHANICALLY OPERATED METERING ROD.
d. Accelerator Pump Circuit.
(1) Purpose. When the throttle valve is suddenly opened, there is a
corresponding sudden increase in the speed of the airflow through the
carburetor. Because the air is lighter than the gasoline, it will
accelerate quicker, causing a very lean mixture to reach the engine for a
brief period. This would result in a severe lag in engine performance if it
were not for the accelerator pump circuit. Its job is to inject a measured
charge of gasoline into the carburetor throat whenever the throttle valve is
(2) Operation. The accelerator pump circuit consists of a pump that
is operated by linkage directly from the throttle valve. There are
passageways that connect the pump to the float bowl and pump discharge
nozzle. Two check valves in the system control the direction of gasoline
flow. Operation is as follows:
(a) The pump is pushed down in the pump chamber as the throttle
valve is opened, forcing gasoline through the outlet passageway.