Is my vacuum advance faulty?

The vacuum advance on the side of your distributor is very easy to test to see if it is working or not.

Vacuum advance is only present for a few moments when throttle is applied, this is why the vacuum port is next to the throttle butterfly. For this reason it is not very easy to test that this is working with the engine running at a certain rpm.

How to test your vacuum advance.
Remove the distributor cap.
Remove the vacuum pipe from the plenum (or carbs).
Suck on the vacuum pipe until you can see the base plate inside the distributor moving.

If you can keep sucking on the vacuum pipe (and the base plate does not move) and not maintain vacuum then this means that the diaphragm inside has split and the unit will need replacing.

We can supply both vacuum advance units for the standard Lucas Rover distributors and the Mallory distributors, please enquire.