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ELECTRICAL SYSTEMS
CRANKING SYSTEM
10-39
generator results in generating a voltage which
prevents the current passing through the mag-
net coil of the solenoid switch relay from con-
tinuing its flow through the generator to
ground, therefore the relay points open to
break the solenoid circuit.
In cold weather, if the first explosions are
too feeble to keep the engine turning over, the
manifold vacuum is not sufficient to cause the
accelerator vacuum switch to break contact,
and neither does the generator develop sufficient
voltage to cause the relay points to open. The
cranking system therefore remains in opera-
tion until the explosions are strong enough to
keep the engine running.
When the engine is running, there are three
separate means of preventing the cranking sys-
tem from being operated by movement of the
accelerator pedal:
(1)
Manifold vacuum acting
on accelerator vacuum switch. (2) Mechanical
lockout in the accelerator vacuum switch. (3)
Blocking effect of generator voltage on solenoid
relay.
TIMING SHIMS
PLUNGER
LIP
TERMINAL CAP
Figure 10-33-Carter Accelerator Vacuum Switch-
Engine Not Running
10-32 ACCELERATOR VACUUM SWITCH
- ON CARTER CARBURETOR
a. Description and Operation
The accelerator vacuum switch used on the
Carter carburetor is built into the throttle body
in position to be operated by the throttle shaft.
The switch consists of a special stainless steel
ball, plunger, guide block, W-shaped contact
spring, and return spring housed in a passage
in throttle body which is closed by a terminal
cap containing two contact blocks. When the
engine is not running and throttle is closed, the
ball rests on a lip on the lower end of switch
plunger and bears against a flat spot on the
throttle shaft. The plunger, guide block, and
contact spring are held in a down position by
the return spring so that the contact spring
does not make contact with the contact blocks
in terminal cap. See figure 10-33.
Figure 10-34-Carter Accelerator Vacuum Switch-
Cranking Position
When the accelerator is depressed with en-
gine stopped and ignition switch turned on, the
flat spot on throttle shaft acts as a cam to push
the switch ball, plunger, guide block, and con-
tact spring upward until the contact spring
makes contact with both contact blocks in ter-
minal cap. This closes the solenoid relay cir-
cuit and puts the cranking system into opera-
tion. See figure 10-34.
Figure 10-35-Carter Accelerator Vacuum Switch-Engine Running
When the engine starts, manifold vacuum
acts on the switch ball and as soon as the ac-
celerator pedal is released the ball is drawn up-
ward a way from throttle shaft. The return
spring then pushes the contact spring down-
ward, thus breaking the circuit and causing
the cranking system to stop operating. See fig-
ure 10-35. As long as engine continues running
the switch ball is held against its seat in throttle
body by manifold vacuum, therefore movement
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