Most lawn mowers use either a Tecumseh or Briggs & Stratton engine. One way to get the highest fuel efficiency from your lawn mower is to set the idle to optimal performance. In order to fine tune the idle on your Briggs & Stratton lawn mower, you must first remove the air filter housing.
Place the Briggs & Stratton lawn mower on a level surface. Remove the screw securing the air cleaner cover over the carburetor with a flat-head screwdriver. Pull the cover, filter and filter housing away from the carburetor.
Find the idle mixture adjustment screw on the side of the carburetor. The screw sometimes has a spring on the stem. Turn the screw clockwise until it just touches the seat of the carburetor. Turn the screw counterclockwise one and a half turns.
Locate the main jet adjustment screw at the base of the carburetor float bowl. Turn the screw clockwise until it touches the carburetor seat and then turn it counterclockwise one and a half turns.
Place the air filter housing, filter and filter cover back over the carburetor. Secure with the single retaining screw. Start the mower and allow it to warm up under half-throttle for five minutes.
Turn the idle mixture screw clockwise with the flat-head screwdriver until the engine begins to slow. Notice the position of the screw and turn the screw counterclockwise until the engine slows again. Turn the screw to the midway point between the two positions that the engine slows.