DATSUN 1970-72 240Z Engine Modification: Testing

Vacuum control valve is set at factory and adjustment is not normally required. If adjustment is needed, proceed as follows:

1. Connect a Vacuum gauge to connector for anti-backfire valve, and raise engine speed to 2, 000 RPM without load. Release accelerator linkage quickly.
2. Manifold vacuum should rise causing control valve to operate and transfer vacuum to servo diaphragm. Servo diaphragm should operate once for a full stroke of 0.197".
3. Following this, both speed and manifold vacuum should reduce. The speed and vacuum should stabilize after one or two seconds. Manifold vacuum at this time is called "Operating Negative Pressure".
4. Loosen lock screw on control valve and adjust vacuum adjusting screw (at end of valve) so that operating negative pressure matches the value obtained from the chart that follows:
5. Make sure that time required to lower speed from 2, 000 RPM to 1, 000 RPM is less than 6 seconds.
   Fig 1: Control Valve Operating Negative Pressure (Operating Vacuum)

   Courtesy of NISSAN NORTH AMERICA, INC.