Two things
One yes. There is an air fuel adjustment, it is a slider on my Furnace it is on the right end of the blower housing, in the burner assembly area.. You said "Thick black" this indicates dang near no air. or.. Another issue,, and alas there are enough "other issues" I am not familiar with for me to even guess.
The othe rsource of odore is a vanishing odor, dust that settles in the system in the summer burns off, but you do not usually see smoke and NEVER from the exhaust.
I'm wondering if you might have an insect nesting in the heat exchanger as well