Vacuum Advance Unit

1. Visually inspect the vacuum advance hose for cracks / leaks, blockage and oil saturation.
2. Remove the vacuum hose from the vacuum advance unit.
3. Connect a test hose with vacuum pump to the vacuum advance unit.
4. Apply 375 mmHg (500 mbar) of vacuum to the unit. Hold vacuum and observe the gauge. Reading should not drop any more than:

37.5 mmHg (50 mbar) per minute

If vacuum loss is grater, diaphragm is bad, replace and retest with new diaphragm.
5. Release vacuum from gauge.
6. Connect an adjustable timing light.
7. Start engine and let idle.
8. Note current timing value. Mark is located on flywheel.
9. Apply vacuum at a steady pace and observe the ignition timing. Timing should advance smoothly.
If not, replace and retest with new distributor.
10. Release vacuum.
11. Apply vacuum. Timing advance should start between:

90 - 120 mmHg (120 - 160 mbar)

If not, replace and retest with new distributor.
12. Release vacuum.
13. Apply vacuum. Timing advance of 10° - 14° over noted idle value should be reached between:

180 - 195 mmHg (240 - 260 mbar)

If not, replace and retest with new distributor.
14. Turn engine OFF.
15. Remove distributor cap.
16. Move the plate on which the Hall sender is mounted counterclockwise. It should move smoothly and spring back into its original position when released.
If not, replace and retest with new distributor.
17. Disconnect all test equipment and reinstall cap and vacuum hose.