In older vehicles that use a carburetor instead of an electronic fuel injection system to deliver the fuel-air mixture to the engine, it is the choke valve’s job to control airflow and make sure the engine starts properly. .
Background: Carburetor Choke
The function of the carburetor is to provide a rich mixture of air and fuel to the engine. When there is too much fuel in the mixture, it is known as “rich” and when there is too much air, it is known as “lean.” Modern electronic carburettors use feedback from sensors to adjust the fuel-air mixture to the level necessary to operate the engine and minimize harmful emissions.
Choke function: what the choke is for
When an engine is started, the air-fuel mixture must be rich, because fuel slowly vaporizes when cold. The choke, which is located on top of the carburetor, will shut off or “choke” the air supply to the carburetor. As the engine warms up, it needs more air, so the throttle plate shaft moves to the side to allow more air flow.
Automatic choke: carburetor choke
Most vehicles use an automatic choke. Typically, a thermostat on the choke will sense the increased heat from the engine that is being transmitted to the choke housing and will cause a bimetallic spring to relax and open the choke valve.