system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does a choke on a carburetor work, and why is it necessary?
gpt
A carburetor is a calibrated device that delivers a set amount of fuel per unit of air passing through it. Cold engines need a richer mix (more fuel per unit of air) to start up. The choke closes to block some of the air from entering the engine to richen the mix and allow the engine to start.