Distributor Vacuum Control: Testing and Inspection

Fig. 13 Vacuum spark advance curve:

1. Warm up the engine fully.
2. Make sure that the idling speed and ignition timing are within specifications.
3. Gradually increase the vacuum on the vacuum advance diaphragm with a hand vacuum pump, note the amount of vacuum when advance starts.

Advance start: 0°/60 mm-Hg (2.36 in-Hg)

4. When the vacuum is further increased, the relation between the vacuum and advance should be kept within range Fig. 13.