Been burning some Turmans and noticed a black and sticky film on inside of stove. I have a Thelin with manual adjustments. These are my second ton, I had to return first ton, for they were total crap, dull color and 2-4 inches long. They threw no heat and caused stove to shut down numerous times, gave a few bags to a friend and they did same to her Harman. These pellets look and burn completly different, but need any info on the black sticky residue, creosote? What if any adjustments may help, I really don't feel like returning these as well. Thanks for any help.