Rebuilt Engine 1st startup: intake port soot?

[Grubby]

I started up my D24t/240 project motor and it ran wonderfully. The engine is a rebuild, and this was its first startup. Afterwards, I took the intake manifold off, and noticed that one of the intake ports had more soot lining it than the rest, which were relatively clean. Not like solid black, just a good dusting of soot. I also noticed in each port, a thin, black drip of something burnt. Any ideas why this might happen? If so, is it typical for this to happen during a break in period, or do I have a problem? I'm probably being really paranoid, but just wondered what people thought.
Any ideas or explanations from you guys would be appreciated.
Thanks,
Abe