RE: volts for ignition?
the engine will go into a "run slow mode" when the voltage gets low, spark energy is at baseline output.
over 6V spark energy will increase 1Kv.. If it is a Falkon unit you CANNOT input more than 6.7v. ZDZ brand with S/N 1511 and higher you may input up to 9v. High operating temps are the biggest culprit for carbon build up. Type of oil and fuel quality are the next biggest culprits. Check baffling and exit air MUST incorporate a spoiler, typical CHT 190-220F. You MUST adj the engine to YOUR elevation, prop and exhaust combination. To leave it a bit rich especially when new is always good.
Thanks,