Can't help you regarding the carbon buildup.
I will pass along what I was told about using modern oil in an old vintage 2 stroke. Don't. I have two vintage motors. One is a British villiars midget cast iron two stroke of 98CCs made in the 1940's or 50's. The other is a German made model 1932 Fitchel & Sachs 2 stroke motorcycle engine of 98CCs. Mine was manufactured in 1934. I was advised by an old fellow who restores Whizzer, Cushman, Sachs, villiars... you name it vintage motors and for mine he recommended Shell Aero 30 weight which is made for aircraft engines. He emphatically said not to use modern synthetics in those antique motors. I was planning to use Opti 2, but respect this man who is recognized internationally for his expertise in restoring these old motors. So I defer to those who know more than I do. My friend Fasteddy and I went in together on a case of the Shell aero which was not cheap and had to be sent away for. Hassle, but I did not want to damage my old motors. I don't know enough to say it is really necessary, but at least I know that the oil I have is good stuff.
SB