I have heard a 'possible' way to get rid of that excessive carbon buildup in your engine.
This, of course, is a very lowbuck solution...! I've never tried this myself yet, but you can 'trickle' some drops of water in your carb with the engine at 2500 rpm or higher. This 'boils' the carbon out of the cylinders somewhat. Care must be taken not to put too much water in at a time because of the danger of a waterlock, but you must be very generous with water if you're able to fill up a 90 cc head-chamber with water at 2500 rpm... Has anyone done this before, so you can clarify if this works as they say it does?
Of course the only proper way to remove the carbon is to pull the heads.
My '62 NewYorker Wagon 413 also pings when the engine is hot... And we even have 98 octane pumpfuel here...! Blocking the heat-crossover passage in the intake manifold does help a lot against pinging. I neglected this when I had the engine apart the last time. And it started pinging after that.. :o(
Herman.