Riding Mowers & Tractors: Why won't my riding mower start?

The ignition switch in a lawn tractor or riding mower supplies power to the electrical components of the engine. If the lawn tractor doesn't turn over when you turn the key to the On position or doesn't shut off when you turn the key to the Off position, you might need to replace the ignition switch.

The ignition coil in a riding mower or lawn tractor produces the energy to cause the spark at the spark plug. The ignition coil is the likely the cause when the engine won't spark if, after you remove the kill wire, there's no spark from a known good spark plug.

The carburetor mixes gas with air before the fuel goes into the cylinder. If the gas/air mix isn't balanced, the engine won't start or the engine will run rough and stall when you try to drive the riding mower. A damaged carburetor may also leak gas. Replace the carburetor if it causes any of these symptoms.

The carburetor mixes fuel with air to create a combustible mixture that enters the engine cylinder and ignites to drive the piston. Impurities in gasoline can clog the carburetor, preventing the engine from starting. Carburetor clogs can also cause the engine to run rough and the engine may stall when you try to drive the riding mower. Seals and gaskets in the carburetor eventually wear out and can leak gas. Use a carburetor rebuild kit to refurbish a clogged or leaking carburetor.

If the riding mower or lawn tractor engine doesn't make any noise when you try to start the mower, it might be time to replace the lawn tractor battery. A good indicator that the lawn tractor needs a new battery is if you charge the battery, and it loses the charge quickly.

The alternator attaches to the engine under the flywheel and generates power for the tractor while the engine is running. The alternator also recharges the battery while the engine runs. If the engine won't start because the battery drains while running the tractor, the alternator could be at fault. Check DC voltage at the battery with the engine running. You should measure between 13 and 14 volts. If not, then you may need to replace the alternator.

The starter solenoid is a coil-activated switch that activates the starter motor. When you turn the ignition key to the start position, the starter solenoid sends current to the starter motor. You'll hear the solenoid click when the ignition switch activates the solenoid. Replace the solenoid if it doesn't click when it gets power from the ignition switch. You'll also need to replace the solenoid if it clicks but doesn't send current to the starter motor to spin the engine.

The air filter traps debris from air entering the carburetor. A dirty air filter could be the problem if the engine stalls after starting or the engine runs rough or sputters. The carburetor won't get enough air to mix with the fuel for combustion if the air filter is dirty. Inspect the air filter regularly and replace it when dirty.

The starter motor spins the flywheel to start the engine when you turn the ignition key to the start position. If the starter motor runs but doesn't spin the flywheel, check the starter motor's drive gear for damage. A defective drive gear won't mesh with the flywheel teeth to spin the engine. Replace the starter motor if you find damage to the drive gear. The starter motor may be defective if it doesn't run when activated. Other failures such as a locked-up engine or poor current flow to the motor can prevent the starter from spinning, so check those issues first. Replace the starter motor if it won't run and you've eliminated other possible failures that could prevent the starter motor from running.

The brake interlock switch detects whether you have the brake pedal fully pushed down. The parking brake holds the brake pedal in the fully depressed position so the brake interlock switch also recognizes whether you have the parking brake set. The brake interlock switch prevents you from starting the tractor without the brake pushed in or the parking brake set. Replace the brake interlock switch if the engine won't start because the brake interlock switch doesn't detect the brake pedal fully depressed or the parking brake set.

The engine fuel filter screens impurities from the gasoline going to the carburetor. A clogged fuel filter won't allow gas to flow to the carburetor so the engine won't start. A damaged filter won't screen impurities from the gasoline, resulting in a clogged carburetor. Replace the engine fuel filter if it's damaged or clogged.