1979 Models

Connect a tachometer to engine, then start engine and allow it to reach normal operating temperature. Disconnect servo diaphragm-to-vacuum control valve vacuum hose at vacuum valve and connect it directly to intake manifold vacuum.
Servo diaphragm is operating properly if engine speed increases to 1650-1850 RPM (1900-2100 RPM on California models) when intake manifold vacuum is applied to servo diaphragm.
If necessary, adjust servo diaphragm adjusting screw to obtain specified RPM. See Fig 3. Turn adjusting screw clockwise to increase engine speed and counterclockwise to decrease engine speed.

Fig 1: Adjusting Throttle Opener Operating Pressure
Courtesy of NISSAN NORTH AMERICA, INC.

Fig 2: 1977-78 Servo Diaphragm Test
Courtesy of NISSAN NORTH AMERICA, INC.

Fig 3: Adjusting Servo Diaphragm
Courtesy of NISSAN NORTH AMERICA, INC.