I have found that after I went to a coil running on volts on my single cylinder engines that have shop made plugs the burning has pretty much gone away. I started winding my own coils that will work on volts. Anyway you are correct in saying that the coil itself is the cause of small plugs...
Welcome aboard I am also from North Dakota I live in Jamestown. My trade was a machine tool designer.
I'm currently working on a 5 cylinder radial engine.
I'm currently working on a 5 cylinder radial engine. This is the first radial engine that I have ever worked on. You can stop by and take a look at various parts I've been working on here InTheShopWithDoc