The 12.5 HP Briggs and Stratton engine has an idle speed adjustment screw below the fuel bowl of the carburettor that can be adjusted in just a few minutes to keep the engine running efficiently. The optimum setting for the carburettor is to run around 1750rpm. You can adjust the carburettor with just a screwdriver and vacuum gauge, helping you to save time and money.
Remove the air cleaner assembly from the top of the Briggs and Stratton 12.5 HP engine and set it aside. Turn the idle mixture screw clockwise with a screwdriver until it is completely closed and turn it back, counterclockwise, one and a half turns.
Put the air cleaner assembly back on top of the engine and start the motor. Let it warm up for a few minutes and slowly turn the idle mixture screw clockwise until you hear the motor slow down.
Turn the idle mixtue screw counterclockwise slowly until you hear it begin to slow down again and turn it back, clockwise, to the midpoint between where you noticed it slowing down. Remove the rubber vacuum hose at the base of the carburettor and attach a vacuum gauge.
Turn the idle speed adjustment screw slowly until the vacuum gauge reads around 1750rpm with the engine running smoothly. Remove the vacuum gauge and reattach the rubber vacuum hose.
Shut the Briggs and Stratton 12.5 HP engine off.
Be careful of hot engine parts when attempting to adjust the carburettor on a Briggs and Stratton 12.5 HP engine.