Air-fuel ratio control system for an internal combustion engine

摘要

An air-fuel ratio control system for an internal combustion engine having a carburetor with a slow speed circuit, includes a feedback control means by which an air intake side secondary air is supplied to the carburetor, on the downstream side of the throttle valve, in response to a result of detection of air-fuel ratio in terms of the oxygen concentration in the exhaust gas of the engine. Under a predetermined operating condition of the engine, the feedback control of the air-fuel ratio by means of the control of the air intake side secondary air is performed while the supply of the fuel through the slow speed circuit of the fuel supply system is controlled in response to the result of the detection of the air-fuel ratio. In a variation of the system, the supply of the fuel through the slow speed circuit is stopped during the predetermined operating condition of the engine.