Plan the perfect garden with our interactive tool →

How to Adjust the Idle on a Briggs & Stratton Lawn Mower

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.

Adjust The Idle On A Briggs & Stratton Lawn Mower

Briggs & Stratton manufactures a variety of small engines for use in lawn equipment, including lawn mowers, roto-tillers, pressure washers and other items. A Briggs & Stratton lawn mower engine uses a carburetor to mix the gasoline and air that is pulled into the cylinder for propulsion. Tighten the idle adjustment screw, found on the side of the carburetor, by turning it clockwise just to the point where you feel it lightly touching the seat of the carburetor. Back the screw off (turn counterclockwise) from this point one-and-a-half turns. Replace the air filter and air cartridge on the carburetor and tighten the set screw clockwise to lock in place. Start the engine, set it to half-throttle and allow it to warm up for about five minutes. Turn the idle adjustment screw slowly in a clockwise manner until the engine's RPMs begin to slow. Remember this position, and turn the screw counterclockwise past the original point, listening for the engine to begin slowing again. Check the engine idle speed with a tachometer. For aluminum-block engines, the engine should idle at 1750 RPM.


You can further fine tune the idle if you have a handheld tachometer. Attach the tachometer lead to the spark plug wire. Turn the idle screw until the engine reaches 1700rpm for an aluminum engine, or 1200rpm for a cast iron cylinder engine.

Garden Guides