At idle and low speeds , the carburetor system supplies enough fuel to the engine to keep it running. When the vehicle gets up to speed (usually about 24 kph or 15 mph) the idle circuit kicks out of operation so that fuel is supplied by the main metering system. Also called the "low-speed circuit."
IDLE CIRCUIT
Meaning of IDLE CIRCUIT in English
English dictionary of automotive terms. Английский словарь автомобильных терминов. 2012