What device is used for cold engine start-up by altering the mixture of gasoline and air?

The choke is designed specifically to facilitate cold engine start-up by adjusting the air-fuel mixture. When an engine is cold, it requires a richer mixture—more gasoline and less air—to start efficiently. The choke restricts the airflow into the engine, which increases the fuel-to-air ratio, allowing for easier ignition. This adjustment is crucial because the fuel atomization is less effective at lower temperatures, and a richer mixture helps overcome this challenge, ensuring the engine runs smoothly when starting.

In contrast, devices like the compressor are not typically used in this context; they serve a different purpose, often in systems requiring pressurized air. The throttle, on the other hand, regulates the engine's power by controlling the amount of air entering the engine during operation but does not specifically assist with cold starts. Lastly, the ignition switch is simply a mechanism for starting or stopping the electrical flow in the ignition system and does not play a role in altering the air-fuel mixture for optimal start-up.