Spark plugs

Oddly no. What you are looking at is not unusual, mine look much the same. I even called Rotec in Canada to ask about it and was told that it’s a characteristic of the carbureted 912.  Afraid I can’t say why though. Perhaps someone who knows can explain.

Cylinder 1 sooty shows that some air is leaking from any joint , may be intake manifold o ring or nuts loose, or carburetor joints loose.

Or spark plugs cable may be faults/worn that leak the current.

Check it properly ?.

As long as I have known anything about spark plugs I have thought that a very light colored plug was running very lean (too much air) and a sooty spark plug was running very rich (too much fuel). Sooty could also mean the plug wasn't firing correctly. An air leak would cause a too lean condition. 

Lately I've seen comments here saying an air leak causes sooty plugs. Have I been wrong all these years?

Alan