A choke is closed when an engine is cold and opened when it is warm, whereas an enrichment circuit is opened when the engine is cold and closed when it is warm. A choke works by restricting the air flow and lowering the pressure inside the venturi, which causes the existing jets to meter more fuel, whereas an enrichment circuit adds extra fuel without restricting the air flow. A choke requires a fast idle cam or something akin to it (or you have to hold the throttle open manually), whereas an enrichment circuit adds a little extra air simultaneously with the extra fuel, so the fast idle is already built in.

Motorcycle carburetors have generally come with cold start enrichment circuits rather than chokes since some time in the '80s (the last carburetor with chokes that comes to mind is the Keihin VB56A found on the '83 Honda CB1100F).