Air-fuel ratio controller for carburetor

In a carburetor of the type having a primary intake passage which operates during normal running of said engine and a secondary intake passage which operates at high-speed operation of said engine, having a main fuel system for supplying a fuel from a float chamber into a venturi formed upstream of a throttle valve rotatably disposed in the primary intake passage, a main fuel control valve disposed in said main fuel system for controlling the flow rate of fuel flowing through said main fuel system so as to converge to a target air-fuel ratio based on a normal running parameter representing a normal running condition of an internal combustion engine, a slow fuel system for supplying the fuel from said float chamber into a portion of the primary intake passage adjacent to said throttle valve, and a slow fuel control valve disposed in said slow fuel system for controlling the flow rate of fuel flowing through said slow fuel system so as to converge to said target air-fuel ratio based on said normal running parameter, an air-fuel mixture being formed by the fuel from both of said main and slow fuel systems and air flowing through said intake passage;

• an air-fuel ratio controller comprising:
• (a) an auxiliary fuel passage communicating said float chamber and a portion of said secondary intake passage downstream of said throttle valve with each other;
• (b) an auxiliary air passage supplying air into said auxiliary fuel passage;
• (c) an auxiliary fuel control valve for controlling the flow rate of fuel flowing through said auxiliary fuel passage;
• (d) an auxiliary air control valve for controlling the flow rate of air passing through said auxiliary air passage;
• and
• (e) an electromagnetic actuator operated by duty-controlled ON-OFF pulses based on at least one of a starting-up/warming-up parameter representing a starting-up/warming-up running condition of the internal combustion engine and a deceleration parameter representing a decelerating running condition of the engine, for controlling said auxiliary fuel control valve and said auxiliary air control valve so as to gradually decrease the flow rate of fuel flowing through said auxiliary fuel passage and gradually increase the flow rate of air flowing through said auxiliary air passage as said at least one running condition proceeds, and to deactivate said actuator for halting or suspending the supply of the fuel and the air from said auxiliary fuel passage and said auxiliary air passage when said at least one parameter indicates that said running condition is completed.