Distributors not equipped with a crank angle sensor are equipped with two methods
of spark advance. They are, an internal centrifugal advance consisting of governor
weights and springs; and an external advance controlled by engine vacuum. Models
equipped with fuel injection are equipped with an electronic advance device.
To test the internal advance:
- Connect a timing light to the engine.
- Warm up the engine to normal operating temperature.
- Check that the idle speed and ignition timing are correct.
- Disconnect and plug the vacuum lines at the vacuum advance.
- Gradually increase the engine speed while checking the timing mark with
the timing light.
- If the mark move to what seems like an excessive amount of advance, the
cause could be a weak governor spring. If the mark moves slowly and seems
like an insufficient amount of advance, the cause could be a governor weight
or advance cam malfunction.
To test the vacuum advance:
- Warm the engine to normal operating temperature.
- Check that the idle speed and ignition timing are correct.
- Disconnect the vacuum lines from the vacuum control and plug them.
- Connect a vacuum hand pump to the vacuum control, slowly apply vacuum and
check the advance with a timing light.
- If the spark advance seems sluggish or not operating, replace the vacuum
control.
To test fuel injected models equipped with an electronic advance:
- Connect a timing light and verify that the timing advances with engine acceleration.
