Re: What exactly does The small coil do?

[Don]

Yep, that driver coil is a simple winding, pretty rugged unless physically damaged by rubbing on the flywheel magnets. But, OMC did "improve" the driver coil in later years for better ignition performance. There was recently a thread about driver coil resistance, but I can not remember the exact spec, differs between manual start and electric start models. I believe the resistance is very low, only a few ohms. You can also check for shorts to ground using the high ohms scale with the driver coil leads removed from the point terminals, you should see an infinite ohm reading when connecting one ohm meter lead to the mag plate, and the other lead connected to either driver coil lead.
Check simple things first, like the ground strap between the mag plate and engine block. Calibrate your ohm meter to the low ohms scale, connect one lead to a good engine block ground, the other to a good mag plate ground. You should see a reading as close to zero as possible. Rotate the mag plate while checking the resistance also, to ensure the ground connection is not intermittent. You could also disconnect the stop switch lead connectors to rule out a faulty stop switch/wiring/circuit. Sometimes the mag plate wiring harness gets shorted or chafed causing a problem as well. And, like Orpilot says, the wobbly mag plates were a big problem.
We all were thrilled in 1977 when the magCD system was introduced on the smaller engines!