Is the black residue on the end of dirt bike a problem?

I have a 04 ktm sx 125 after I ride there's is always black residue on my exhaust pipe it has a fmf fatty with a shorty silencer people tell that all two strokes do that but my friend has a 09 ktm sx 150 and his never does I use silkolene at 40:1 he uses amsoil 50:1 I want to stay with that ratio because that's what silkolene recommends but is the black residue an issue?