If you ;eave the coil energized for a long period of time and the points are in the right position...I think its when they are closed so juice flows through them...the coil will constantly be energized and dumping power...this WILL burn out the coil.
If I am wrong, it happens when there is a gap in the points but be assured, it does happen...been there.
Have you ever checked the timing? The stock 230 can run a lot of timing advance and still run well...if you are outside those parameters, maybe it could act this way...
Is it backfiring out the carb or the exhaust? I have always heard if its out the carb, its timing...if its out the exhaust, its fuel...
Lord send your Holy Ghost into our hearts and make the desire of our hearts Your Will.
Pro-choice, that's a LIE, babies don't choose to die!!