| 摘要 |
A system for controlling the air-fuel ratio of an air-fuel mixture for an internal combustion engine having a two-barrel carburetor. The system is provided with an O2 sensor for detecting the concentration of oxygen in the exhaust gases, an on-off electromagnetic valve for correcting the air-fuel ratio of the air-fuel mixture supplied by the carburetor and an electronic control circuit. The electronic control circuit operates to compare output signals of the detector with a stoichiometric value, and to produce driving pulses for driving the on-off electromagnetic valve and for controlling the air-fuel ratio to a value approximately equal to the stoichiometric air-fuel ratio. A fixed signal generating circuit is selectively connected to the electronic control circuit. The two-barrel carburetor has an actuator actuated by the vacuum at the venturi of the carburetor for opening a throttle valve of the secondary side of the carburetor. A first vacuum switch is provided to be operated in response to the vacuum in the intake passage and a second vacuum switch is provided to be operated by the vacuum in the secondary side of the carburetor. When one of vacuum switches is operated, the fixed signal generating circuit is connected to the electronic control circuit for providing a fixed duty ratio for the valve and renders the electronic control circuit non-responsive to the output of the O2 sensor.
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