Home › Forum › Ask A Member › What exactly does The small coil do? › Re: What exactly does The small coil do?
That is the driver coil. As I recall it outputs about 200 volts depending on the model that it sends to the primary circuit of the ignition coils. The igniton coils then boost it to 15 to 20,000 volts. It’s basically the precursor to CD igniton systems, one of several "innovations" OMC came up with to keep their early 9.9 and 15’s from fouling plugs at trolling speeds. Having worked as an OMC tech during that period I can tell you the ’74 to ’76 models were generally a pain in the keister. It wasn’t till the CD ignition came out in ’77 that the problems were fully resolved.
As to your intermittent ignition problems, short of bench testing the ignition coils, the first thing you can do is check for continuity of the secondary circuit of the ignition coils – one lead to ground and one lead to spark plug terminal. If it doesn’t show a circuit there, try moving the plug terminal around to see if that’s the culprit. My experience was that the driver coils didn’t fail that often. The other problem common with those models was loose armature plate bushings that allow the points to wander around in their setting which of course effects ignition timing, usally showing up as a rough idle.