I have got in the past ignition coil overheating, making the engine run very erratically and in some cases it even wouldn't run at all until the coil got cooler. In one occasion I changed the coil for a new one and it overheated as well.
Isolating the problem by excluding heat transfer from the engine, bad grounding and + feeding, bad condenser or break points, what other things could cause this?
I have read about: wrong timing, wrong spark plug gaps, dirty spark plugs (not in my case), poor fuel/air mix.