Description

Vacuum Advance Unit for the ignition distributor on the 3.5L V8 petrol engine.

This vacuum capsule mounts on the side of the distributor and connects by a small pipe to a vacuum take-off at the carburettor or inlet manifold. Under light load, vacuum draws the diaphragm against its spring and the linkage rotates the distributor pick-up base plate to advance the ignition timing, improving part-throttle efficiency; as load increases and vacuum falls the timing returns.

A ruptured diaphragm or seized linkage shows up as poor part-throttle running, pinking, or loss of economy.