Figure 4-39. Automatic Choke System.
is to supply heat to the choke mechanism. The choke
amount against the force of the thermostatic coil.
housing also is connected internally to a manifold
Manifold vacuum usually is used to operate this device,
vacuum source. As the engine runs, manifold vacuum
which is usually in the two following configurations:
draws air through the heat tube and the choke housing.
(1) Choke Piston (Fig. 4-44). The choke piston
The heat tube passes right through the exhaust manifold
so that as it takes in fresh air via the choke stove, it will
is integral with the carburetor, as is the passage that
pick up heat from the exhaust without sending any actual
supplies vacuum to it. The vacuum passage is situated
exhaust fumes to the choke mechanism. Actual heating
on the side of the piston cylinder so that it will only pull
of the fresh air entering the heat tube occurs in the choke
the choke valve open the desired amount before the
piston will cover the vacuum passage. This will block the
passage, keeping the piston from moving any further.
f. Regulating Choke Valve Opening. As with the
(2) Choke Piston Integral with Choke Housing.
manual choke system, a device must be incorporated
Figure 4-40 Electric Choke