The primary byproducts of proper combustion are Energy and water vapor. On humid days, moisture in the atmosphere passes right thru the engine, sucking up heat to become steam, and then most of it will condense in the exhaust system and puddle in your muffler. If you don't provide drainage, acids will form in there and it will soon have holes in it. But after awhile, the exhaust moving thru, will pick it up and eject it out the tailpipe as black sooty droplets. The steam will condense in every low spot in the exhaust system.
The steam will also clean out your combustion chambers, moving the soot out the back.
I run my engine at 205
I hope you have a working vacuum advance. This will allow you to lean out the PartThrottle and cruise circuits. On the hiway, on long trips, the engine should stop producing soot, and either clean the tailpipe right out, or it will begin accumulating a hard brown deposit; either is good. But a powdery white deposit is not good.