My Toro Mower Has a Low Engine Rev

Choke and Throttle

• Toro mower engines, including the Kohler brand engines used on Toro's garden and lawn tractors, have choke control systems that increase the fuel ratio for ignition. This aids the Toro mowers in starting cold engines. If the choke is not all the way open due to mechanical failure, the fuel supply is limited, reducing the engine’s RPMs. Limited throttle controls will also keep the engine at low RPM. Mechanical failures can prevent transition from idle speed to fast.

Fuel System

• Your Toro engine’s fuel systems are responsible for keeping fuel flow throughout combustion and operation. Interruptions in fuel flow limit the engine’s ability to operate at higher RPMs. If the gas tank has a ventilation cap, it must be clear of debris so air pressure can fully force fuel into the fuel lines. Fuel lines and the fuel filter must also be free of obstructions such as sediment and sludge buildup. A failed fuel pump won’t push fuel into the carburetor for vapor creation.

Carburetor

• The carburetor mixes the fuel and air to create an ignitable vapor in the combustion chamber. Certain carburetor adjustments such as the needle setting ensure the proper ratio is created. A bad float valve prevents the carburetor from adjusting fuel flow. Damage to the carburetor’s main circuit will prevent it from allowing a larger mix as needed for high RPMs. Carburetors also get clogged if old or corrupted fuel passes through it.

Spark Plug Condition

• The spark plug in your Toro engine ignites the fuel air mixture as the flywheel generates voltage to pass through it. The combustion cycle happens 1,000 times per minute. Spark plugs, however, must have the right gap setting so the electricity has enough room to reach the vapors. An incorrect gap setting can limit that ability. Too narrow a gap prevents electricity from coming out, while too wide of a gap shortens its reach. Check the spark plug gap setting according to the owner’s manual at least once a season. Replace the spark plug every season.