Throttle Operation; Accelerator Pump; Idle System Diagram - Ford VSG-411 Service Manual

Fuel System
3-13
FIG. 13 Idle System
A - Main Pick Up Tube
B - Idle Fuel Jet
C - Idle Air Jet
D - By-Pass Gallery
E - Sonic Discharge Tube
THROTTLE OPERATION
The same basic carburetor is used for all engines. Therefore
it can be seen that the throttle bore has to be sufficiently large to
pass the air requirements for the larger engines to meet its
FIG.
14
Progressive Throttle System
power needs. However, on the smaller engines maximum air
requirements can be achieved with only 75% of throttle. This
could make initial opening very sensitive.
To overcome this the throttle linkage has been made progressive
with a cam and roller mechanism so that a large initial throttle
movement will only give a small throttle plate opening. As the full
travel is approached the throttle plate movement is very rapid.
ACCELERATOR PUMP
The accelerator pump is vacuum controlled. The system senses
the fall in manifold vacuum and injects fuel directly into the
venturi, enriching the mixture and minimizing any hesitation.
Under normal operating conditions a vacuum, obtained from be-
neath the throttle plate: is available at the pump and pulls a
diaphragm back againstta spring load. This in turn draws fuel,
through internal galleries, from the float chamber. In this situation
the pump inlet one way valve is open and the outlet one way valve
is closed (Figure 15).
The system also includes a back bleed, located in the pump, and
a vacuum break air hole, located at the fuel outlet. The function of
each is detailed later.