Few days before I have few races, so the day after that I go see spark plugs. Colour is ok, dark brown, but I noticed few bits on electrode. It is very small silver bits... I have fear that maybe means knocking...

Can that be from knocking (from piston) or can be something else, from fuel, oil... ?

I have standard engine, just chipped (superchips) and run 14 psi (about 1 bar peak, holding 0.7 bar). Fuel mixure under boost is very rich, about 11.5 to 12:1. I use 100 octane fuel.

I also grab with screwdiver on piston, and have black coat on it.