PURPOSE: To prevent rattle and stop of an engine during rapid acceleration from an idling state and rapid deceleration from the wide opening of a throttle to the idling state.
CONSTITUTION: A carburetor has both a main metering nozzle 26 and an idling circuit 58, 66, 68, 28 supplied with liquid fuel from the same metering chamber 40, and an accelerator and shut-off assembly 60 in the idling circuit. The assembly 60 has a valve 74 of which a passage 66 is open to supply fuel to the idling circuit when a throttle 16 is in an idling position. When a throttle shaft 18 is rotated to open the throttle 16, a piston 70 is advanced. The valve 74 is advanced to close the passage 66 to shut-off the supply of fuel from the metering chamber 40. When the throttle is open, the fuel in a pocket 79 is forced out to be supplied to idling ports 30-36 through a passage 68.