Figure 4-39. Automatic Choke System.

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Figure 4-37. Choke Valve Operation.

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TM-9-8000 Principles of Automotive Vehicles Manual

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Figure 4-41. Engine Coolant Heated Choke.

TM 9-8000

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

stove.

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

that

will

open

the

choke

measured

The

choke

piston

system

also

may

Figure 4-40 Electric Choke

4-25