Duty Solenoids
The duty solenoid(s) are solenoid valves that are operated by the control unit. The solenoid(s) open and close at a constant rate of about 40 cycles per second, though the "ON" time can vary. When the engine is being monitored by the oxygen sensor and control unit (closed loop), the average "ON" time is 30-40%. This time determines the air/fuel ratio and can be measured using a dwell meter.
The duty solenoids for the 2-bbl. carburetor are located on the intake manifold and are connected to the carburetor by air hoses. A small air cleaner is provided to filter the air which enters the carburetor through the duty solenoids. The duty solenoid for the 1-bbl. carburetor is mounted on the air horn of the carburetor.