A dual vacuum break choke is used on inline six and some 4 bbl carbureted V8 engines, starting in 1975.
Once the engine has reached a specified temperature, the secondary vacuum break pulls the choke to almost wide-open position. Vacuum to the secondary break is controlled by a coolant temperature operated vacuum valve on V8 engines, and by an electrical thermoswitch and solenoid on inline sixes.
- The solenoid is located next to the choke vacuum diaphragm. Remove the connector from the solenoid.
- Connect one of the solenoid terminals to the battery and ground the other terminal. If the solenoid doesn't click when the connection is made, the solenoid is defective and must be replaced.
- Leaving the solenoid connected as in step two, unfasten the hose from the secondary vacuum break and engage a vacuum gauge to it.
- With the engine running and the solenoid energized, the gauge should read zero.
- Disconnect the jumper wires and the gauge should read full manifold vacuum.
- If these conditions are not met, the solenoid is defective.
- Reconnect the solenoid electrical connector