Vacuum Advance/Retard Operational Test

1. With the engine idling at normal operating temperature 176°F, (80°C) pull the vacuum retard hose from the distributor connection. the engine speed should increase.
2. Re-connect the retard hose, then bring the engine speed up to 3000 rpm and hold it there.
3. Pull off the vacuum advance hose from the distributor connection, and the engine speed should decrease.
4. If the engine speed does not change, check:
a. The vacuum advance/retard unit
b. Distributor breaker plate
c. All vacuum hoses and connections
d. Check the vacuum source (vacuum available at the right place at the right time).