Smoking can be caused by a few different phenomena, including bad/stuck piston rings, an old or improperly gapped spark plug, a failing spark plug wire, and an especially dirty carburetor. Start by making sure the spark plug and plug wire are in good shape and that the spark plug is gapped according to the manufacturer’s specifications. Then add a can of Berryman B-12 Chemtool Fuel System Cleaner (part #0116) to the gas tank and spray Berryman B-12 Chemtool Carburetor, Choke & Throttle Body Cleaner to spray into the carburetor while the mower is running.