Feedback Carburetor System: Operation
The "X" system is the main feedback system. It controls air/fuel mixture by controlling the opening of air control valve B according to the amount of vacuum at the diaphragm chamber of the valve. The frequency solenoid B is modulated by the control unit, and controls the amount of vacuum to air control valve B. On Civic models, a feedback control solenoid is provided to stop feedback operation under low engine speed and cold engine temperature.
Mixture is more finely controlled by the "M" system, based on engine load. The diaphragm chamber of air control valve A receives the same carburetor vacuum as the EGR control valves A and B, and air is supplied to the intake manifold in proportion to the carburetor intake air volume. Frequency solenoid valve A receives signals from the oxygen sensor through the control unit and opens the valve when air/fuel mixture is richer than pre-set (stochiometric) mixture.