Why is the exhaust stack of my engine black with soot after using auto gasoline?
A black soot is the natural by-product of burning unleaded gasoline and is to be expected. This is not an indication of a rich mixture, nor an indication of internal build-up or potential for spark plug fouling. The black soot is graphite-type deposit. The gray deposit we usually see when using 100LL aviation gasoline is a lead-type deposit.
