Ignition System - HEI (CARBURETED Models): Operation
The pick-up coil assembly consists of a permanent magnet, pole piece, and a pick-up coil. The pick-up coil assembly is stationary, unless shifted by the vacuum control unit. The timer core position can also be shifted by centrifugal weights.
When timer core external teeth line up with internal teeth of pole piece, voltage is induced in the pick-up coil. This signals the electronic module to open ignition coil primary circuit. See Fig 1. This causes low voltage in ignition coil primary circuit to collapse and induce high voltage while traveling across coil secondary windings. Voltage travels through rotor, distributor cap and secondary wires to fire each spark plug.
The electronic module controls dwell period and is not adjustable. Periodic checks of dwell is unnecessary. The HEI system features a longer spark duration, which is desirable for firing lean and EGR-diluted mixtures.