The fuel mix changes thru throttle settings. That sooty look mite be from when the plug is firing at "above idle" & idle is lean enough to pop, and/or
you may not have all the leaks fixed.

Im not a great tuner of carbs, at all, so, someone may come along & totally dismiss what I said. Take what I said with an eye to someone else for confirmation. I wouldnt do anything based on what I think unless someone I know knows what theyre talking about agreed.

Executioner, check out the café posts.