How does a carburetor's choke mechanism affect idle mixture?

27 Eyl 13:45

Can someone explain how the choke valve in a carburetor influences the air‑fuel mixture during cold starts and idle? I understand it restricts airflow, but I'm unclear on the exact effect on mixture ratio and how the transition back to full opening is controlled. Also, what are common tuning tips to avoid a too rich or too lean idle when the choke disengages?