I have an older furnace that has been smelling funning when running, maybe gas, not sure.Black soot has been starting to collect inside my furnace and exhaust pipes. My carbon monoxide detector is not registering more than 18ppm. I can't see any cracks in my heat exchanger, and there doesn't seem to be any smell coming through the register vents. The flames in the furnace seem to be rather high and mostly orange. I tried to adjust the air mix on the front of the burners but it didn't to do much to change the flames. Any ideas why the smell and soot collecting recently?

Your burner is not working properly. It could be a defective regulator among other items. I highly suggest you call for ON SITE service on this one.