Vacuum Advance

Fig. 11 Testing vacuum advance:

1. Warm up the engine fully.
2. Make sure that the idling speed and ignition timing are within specifications.
3. Disconnect the vacuum hose from the vacuum control unit and plug the hose Fig. 11.
4. With engine at idle, attach a vacuum pump to the control A and B

Fig. 12 Vacuum spark advance curve:

5. Gradually increase the vacuum on the vacuum advance diaphragm while noting timing light, note the amount of vacuum when advance starts.
6. When the vacuum is further increased, the relation between the vacuum and advance should be kept within range Fig. 12.