Rich or Lean?

Do you have a choke? If you do, set it to pull off a little faster. They are close. If you're in a climate like CT, leave them. Because when it's cool, it will be perfect, and when it's warm, it's not really that rich. If this were a tuning for the track deal, I think it's a hair rich. Maybe not jetting, but power valve timing or too much squirtor or too slow a choke setup. Modern cleaner fuels and good quench and tight chambers should not have much or any carbon present, but a choke equipped, or one that idles a lot, or where the carb might not be perfectly tweaked will look just like that. Detonation is when the conditions in the engine or the fuel allow for a 2nd flame front to develop when the mixture is fired. As these two fronts meet, tremendous stress is introduced to the chamber, head gasket, piston, rods, bearings, crank, and block. It is not always audible, but by careful looking, you'll see bits of piston material that is hammered off the piston and sticks to the ceramic. You need a magnifier to see it, and as mentionned, you see tiny flecks of silver or bluish black spheres stuck to it.