Accelerating Pump System - Ford VSG-411 Service Manual

03-9
Fuel System 03-9
ZENITH MODEL #33 CARBURETOR (Continued)
Accelerating Pump System
The accelerating pump controls the amount of fuel that is
discharged into the air stream on sudden throttle openings.
When the throttle is opened suddenly, air rushes through
the carburetor into the intake manifold and to the engine.
This air is lighter than the liquid fuel and gets into motion
more quickly. That means that the air reaches the cylinders
of the engine before the first charge of fuel supplied by
the high speed system. A lean mixture would result
momentarily in this case, and to counteract the condition,
additional fuel must be supplied instantly. The supply of
that extra fuel is the job of the accelerating pump system.
ACCELERATING
JET
SPRING
\
PROTECTOR
CHANNEL
ACCELERATING SYSTEM
The accelerating system consists of the pump diaphragm
assembly, accelerating jet, intake check valve, and three
parts making up the refill check. The pump is vacuum
operated. In this system the pump diaphragm is pulled
against the pump spring by the engine manifold vacuum.
When the throttle is opened, the pull on the diaphragm
drops allowing the spring to push the diaphragm against
the fuel causing it to discharge through the accelerator jet.
This amount may be varied by adjusting the travel of the
pump spring. Such adjustment is made possible by
changing the length of the diaphragm protector in the end
of the pump spring.