Air-fuel ratio control system

摘要

An air-fuel ratio control system for an internal combustion engine having a two-barrel carburetor comprising a primary side having a main metering system and a slow speed system and a secondary side having a main metering system. Two on-off electro-magnetic valves are provided for correcting the air to be supplied to air bleeds of both the primary and secondary sides for correcting air-fuel ratio of the air-fuel mixture supplied by the carburetor. A first passage is provided for connecting the slow speed system of the primary side to one of the electromagnetic valves, a second passage is adapted to connect the main metering system of the secondary side to the one of the electromagnetic valves; and a third passage is provided connecting the main metering system of the primary side to the other electromagnetic valve. A change-over valve is provided for changing the connection between the electromagnetic valve and first and second passages. The change-over valve is so arranged to normally communicate the electromagnetic valve with the first passage and to communicate the electromagnetic valve to the second passage when the secondary side becomes to operate upon heavy load.