Briggs & Stratton manufactures gasoline-powered engines commonly used on lawn mowers and other gardening equipment. Although the engines are designed for long life with a simple maintenance routine, over time you may see and smell black smoke. This is a sign that you need to adjust the engine so it will operate at peak performance. Black smoke can be caused by the carburetor, but is typically due to a fouled air filter or dirty oil in the crankcase.
Remove the screw on the top of the air filter canister on the side of the Briggs & Stratton with the engine turned off. The five-sided canister sits directly over the carburetor on the right-hand side of the engine, when looking at the Briggs & Stratton from the rear.
Lift off the canister containing the air filter as well as the long mounting screw that holds it over the carburetor.
Twist the idle mixture screw on the carburetor clockwise until the screw head is just above the rubber seal on the carburetor. The screw is located inside the carburetor as you look down into the part.
Rotate the screw counterclockwise one complete turn with the screwdriver and another half turn.
Remove the cover from the metal canister to expose the air filter. If your engine uses a disposable paper filter, replace it with a new one. If you have a sponge-like filter, continue troubleshooting.
Clean the air filter with water and liquid soap, scrubbing the bottom of the filter where dirt and grass clippings accumulate. Over time, the filter can become clogged, causing the engine to smoke.
Squeeze excess water from the filter. Allow it to dry. Pour 1 tbsp. of engine oil on the filter. Squeeze out the excess oil.
Replace the filter in the canister and reattach over the carburetor using the screw removed in step 1.
Start the engine normally and run at idle speed for a few minutes to determine whether the engine is still smoking. If the smoke persists, continue troubleshooting.
Unscrew the oil cap on the base of the engine and turn the Briggs & Stratton on its side to catch some of the oil on an old rag. Run your finger over the oil. Good engine oil is a caramel color. If the oil is black or feels coarse and gritty, drain the old oil from the engine by turning the Briggs & Stratton upside down.
Fill the engine crankcase with fresh motor oil and replace the cap before testing the engine. Use an oil weight and quantity recommended for your particular engine. The recommendation is printed on the side of the Briggs & Stratton.