OK, well you have the infamous OMC “low tension ignition system”….Kind of a “hybrid” between the original OMC universal magneto and the CDII system that would come in 1977. This system is often hated, mostly due to a lack of understanding…
Yes, I would update/change that driver coil unless it seems relatively new, there was many internal changes/improvements made to that piece. The driver coil is a single winding that generates the primary voltage for both coils. But, before you replace it, you need to check for side to side slop on the magneto plate, this is a common problem. If the mag plate is sloppy from side to side, or up and down, point gap will vary and ignition output will be poor. The other issue is the air gap between the driver coil laminations and the flywheel magnets. This must be properly set with an alignment tool. Slop in the mag plate will also result in having the flywheel magnets rub on the driver coil. But, if the driver coil is set in too far from the flywheel magnets, primary output will be weak also.
Sounds like you already have replaced the the external coils. But, there are a few other things to consider. First, there is a black ground strap the runs from the mag plate to a good ground on the block. This should be checked using an ohm meter on the low scale. Twist and turn the mag plate also, to ensure the lead isn’t chafed/broken/intermittent. The same issues occur with the wiring harness that runs out of the mag plate to the coils. Those leads can get chafed/split/grounded.
Finally, and I should have lead with this, is the stop switch. Pressing the stop switch shorts both sets of points together, killing primary output. So, it is best to disconnect the two stop switch leads from the ignition harness to make sure the switch is not faulty. It is also possible that the stop leads that are connected to the breaker points are grounded/chafed onto the mag plate. So, you may want to disconnect the stop leads right at each set of points and recheck to rule out that possibility…
It is also important to realize that both sets of points must be set and working correctly, or you could lose spark to both/opposite cylinder. The primary voltage completes its path back to the driver coil through the opposite set of points that is closed….So, let’s just say one set of points was not closing properly, or perhaps oil soaked…You might lose spark to the opposite cylinder because its primary signal can’t make it back to the driver coil through the points from the other cylinder….
