Black soot in HE furnace vent

Brand new furnace. What would cause this? Never seen anything like this before.
Thanks in advance.

Incomplete combustion.

Improper combustion…various potential reasons.
Oh, hi Dave. I took longer to post than I planned.

Thanx y’all. Have a great weekend!

Hay Larry,

Feel free to expound on my 2 words. (That’s why I beat you! ;-), just 2 words).
I have no time for it.