The choke is simply a flat disc mounted on a shaft at the carburetor air inlet. When you turn on the choke, the shaft is rotated so that the disc blocks the airflow, and there is greater suction in the inlet. This makes it possible to vacuum more fuel and also makes it easier to start. Chokes are usually automatic but can be manual on some engines. In this case, they must be turned on when starting an engine and then turned off after the engine has been running for several seconds. If an engine is hot, leaving the choke will probably flood the carburetor and cause difficulty starting.
Carburetor air intake showing choke plate (air filter has been removed) on a small 3 1/2 HP Briggs and Stratton engine.
Carburetor Air inlet showing choke plate (air filter removed) on a small 3 1/2 HP Briggs and Stratton engine.
