Fuel Delivery and Air Induction: Description and Operation

Fig. 4 2150A feedback fuel control:

This carburetor feedback fuel control, utilizes a pulsing solenoid to introduce fresh air from the air cleaner into the idle and main system vacuum passages to lean the fuel and air mixture from the maximum rich condition (0% duty cycle-solenoid closed) to the maximum lean condition (100% duty cycle-solenoid fully open). The solenoid operates under the control of the EEC-IV system. This carburetor also incorporates a throttle position sensor, Fig. 4.