Choke (Cold-Start Enrichener)

The choke is a cold-start device on carburetted engines. A cold engine needs a richer mixture because fuel condenses on cold surfaces instead of vaporising. A true choke is a butterfly valve that restricts air at the carb inlet; many motorcycle carbs instead use an enrichener or starter circuit that adds extra fuel through a separate jet. Both are commonly called "the choke".

Use it only when starting cold and turn it off gradually as the engine warms, usually within a minute or two. Riding with the choke on wastes fuel, fouls the spark plug and can wash oil off the cylinder walls.

Fuel-injected bikes have no manual choke: the ECU enriches the mixture automatically, sometimes with a fast-idle lever. If a carb bike only runs with the choke on, the pilot jet is probably blocked or there is an air leak.