1976 1300cc & Calif. 1600cc Equipped Models (Vacuum Control Valve Test)

Remove air cleaner. Disconnect intake manifold vacuum hose going to vacuum control valve. Connect vacuum gauge to system. On California 1300cc engine, disconnect and plug vacuum hose from anti-afterburn valve.
On all models, start engine. Increase engine speed to 3000 RPM and quickly release throttle. Vacuum gauge highest reading should be obtained immediately after releasing throttle, drop to 22-23 in. Hg, and then slowly drop to idle vacuum.

Fig 1: 1979 Throttle Positioner System
Courtesy of MAZDA MOTORS CORP.

Fig 2: 1977-78 Servo Diaphragm Test
Courtesy of MAZDA MOTORS CORP.
If vacuum reading is incorrect, turn adjusting screw in vacuum control valve. Decrease vacuum reading by turning screw clockwise; increase by turning screw counterclockwise.