Fuel Delivery and Air Induction: Description and Operation

Fig. 7 High altitude emission control system:

This system, Fig. 7, comprises an altitude sensing switch, solenoid valve, air cleaner and three carburetor metering orifices.
To avoid an excessively rich carburetor mixture at high altitudes (due to decreased air density), the system supplies additional air through the carburetor metering orifices. At a predetermined altitude, the altitude sensing switch will close the circuit between the battery and solenoid valve.
For high altitude emission control system diagnosis procedure, refer to ``Computerized Engine Controls'' section