How a Choke Works Integral Type

posted in: carburetor | 5

When the engine is cold a richer fuel mixture is needed. As it warms up the mixture must be leaned out. This is where the automatic choke circuit comes into play.
Choke ThermostatChoke Thermostatic Coil

The choke shaft extends through the carburetor into a round housing. Inside the housing there is a thermostatic coil spring. This spring will wind & unwind depending on the temperature. When cold the thermostat will hold the choke valve closed. As the temperature warms up, the spring expands and allows the choke valve to open.

Vacuum BreakChoke Vacuum Piston

The choke vacuum piston is linked to the choke butterfly by a small linkage. At idle, which will have full vacuum, the piston will be pulled into the piston well. This puts pressure against the thermostat coil trying to open the choke valve slightly.

Offset Choke Valve

Not all carburetors will have this air valve. Marvel Schebler & the Holley 1 barrel carburetors are a few examples that do. The air valve is placed offset on the choke valve. This keeps the choke from causing a too rich condition.

stove PipeStove Pipe

Most automatic chokes systems will use a stove pipe to heat up the thermostat coil. The pipe heats up, using the exhaust manifold and the heat is then pulled up to the thermostat using vacuum from the carburetor, which is fed by the intake manifold.

5 Responses

  1. Hello,
    I have a friend with a 1980 Plymouth arrow truck that is in need of a carburetor and having trouble locating one.
    It is the 2.0l 4 cyl.
    He would like a new carburetor of possible. Do have any leads?

  2. David Weiss

    Hey Mike! I have a 1908 Holley on a ’62 Rambler that is leaking fuel up from top of the bowl. It is the first time the car has been turned over since the fall and I wonder if the choke needs adjustment as it seems to be flooding. How do I make this adjustment?

    Please advise!



    • Your problem is most likely varnish and you will need to remove the carburetor, clean it well and replace the rubber parts.

  3. Wesley Edens

    I am thinking about installing an electric choke on my buick 300 engine. Is this a good or bad idea as to performance?

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