Vacuum Solenoid Regulator
The regulator provides the vacuum signal to the feedback carburetor. A solenoid and regulator are combined in one housing. When the solenoid is de-energized, the output port is blocked and vacuum is vented to atmosphere. When the solenoid is energized, vacuum passes to the carburetor. The average "ON" time versus "OFF" time determines the vacuum level provided.
When the oxygen sensor and control unit sense a rich mixture, the solenoid is "ON" longer, producing a higher vacuum signal. This allows more air through the idle circuit, and less fuel through the main mixture circuit. For lean conditions, the vacuum signal is lower.