Why did my riding lawn mower stop working?

If your riding lawn mower suddenly stops running, there are a few common issues that could be causing the problem. In this article, we’ll discuss some of the most likely culprits and how to troubleshoot them.

Check the Fuel Supply

One of the first things to check when your riding mower won’t start is the fuel supply. Here are some potential fuel-related issues:

• Empty fuel tank – If the fuel tank is empty, the engine won’t be able to run. Check the fuel level and refill the tank if needed.
• Clogged fuel filter – The fuel filter screens out debris that could clog up the carburetor. If it’s clogged, fuel can’t flow properly to the engine. Remove and replace the filter.
• Faulty fuel pump – Most riding mowers have a mechanical or electric fuel pump. If this pump fails, fuel won’t be delivered to the carburetor. Test the pump and rebuild or replace it if needed.
• Stale fuel – If fuel sits for too long, it can go bad and cause issues. Drain the tank and replace with fresh gasoline.

Start by checking the fuel level visually in the tank. If that looks ok, move on to ensuring fuel is reaching the carburetor. You can confirm fuel flow by disconnecting the fuel line and cranking the engine to see if fuel spurts out.

Check the Ignition System

For gasoline engines to run, the ignition system must be generating a spark to ignite the fuel. Problems with the ignition system can prevent starting:

• Faulty spark plug – The spark plug may be fouled or damaged, not allowing it to fire properly. Replace the spark plug.
• Spark plug boot issues – The rubber boot covering the spark plug can become cracked and lead to spark plug misfires. Replace the boot if damaged.
• Faulty magneto – The magneto uses magnets and coils to generate high voltage for the spark plugs. If it’s malfunctioning, it won’t supply adequate voltage. Test and rebuild or replace the magneto.
• Disconnected or damaged spark plug wire – Damaged spark plug wires can interrupt the path to the spark plug. Visually inspect wires and replace any damaged ones.

Testing the ignition system involves removing the spark plug, reattaching the wire, and grounding it while cranking over the engine. You should see a blue spark within the cylinder. If not, additional ignition system testing is required.

Check the Engine Compression

Sufficient compression in the engine cylinders is required to ignite the fuel mixture. Low compression can cause a no-start condition. Here are some compression-related issues:

• Blown head gasket – The head gasket seals the combustion chamber. If it fails, compression leaks down past the gasket lowering cylinder pressure. Replace a blown head gasket.
• Stuck or bent valves – Valves must seat properly to achieve compression. Sticking valves or bent stems prevent this. Inspect and repair any valve train issues.
• Worn piston rings – The piston rings seal against the cylinder walls to create compression. Over time they wear and lose their seal. Worn rings require an engine rebuild or replacement.
• Cylinder bore wear – Excessive wear of the cylinder walls from extended use reduces compression seal. This requires a cylinder reboring or engine replacement.

Use a compression tester in the spark plug holes to measure the compression readings. Compare to manufacturer specifications. Significantly low readings indicate internal engine issues.

Inspect the Blades and Mowing Deck

The mower blades and deck can also cause issues that lead to stalling. Check the following:

• Blade obstruction – Buildup of clippings or other debris can clog the deck and blades, increasing drag on the engine leading to stalling. Clear any obstructions.
• Improperly installed or damaged blades – Damaged, unbalanced, or backwards blades can jam the deck. Ensure blades are in good shape and installed correctly.
• Deck height too low – Adjusting the deck too low reduces air intake and increases strain. Raise deck height to factory settings.
• Damaged or worn deck bearings/pulleys – Worn or damaged components increase resistance on the blades. Check and replace any faulty parts.

Manually spin the blades to ensure they rotate freely without catching or significant drag. Also ensure the deck raises and lowers properly on the adjustment mechanisms.

Check the Safety Switches

Riding mowers have safety interlocks and switches to cut power when a safety issue arises. Here are some of the main safety systems:

• PTO/blade engagement switch – If damaged, it may power off during use. Test the function.
• Seat safety switch – Only allows operation if an operator is detected in the seat. Ensure not obstructed.
• Brake pedal safety switch – Puts the brake on and cuts power if pedal is released. Test for proper operation.
• steering column tilt switch – Disables mower if the steering wheel is tilted up. Check for correct adjustment.
• Parking brake safety switch – The parking brake must be disengaged to allow starting and operation. Confirm it’s functional.

Bypass and test each safety switch one by one to see if you can replicate a stalling issue. Replace any faulty safety switches found.

Check the Drive Belt

On belt driven riding mowers, issues with the mower drive belt can also lead to stalling. Inspect the following:

• Belt tension – A loose belt will slip and not adequately power the cutter deck. Adjust belt tension accordingly.
• Worn/damaged belt – Belts can wear out over time. Swap in a replacement belt if needed.
• Debris buildup – Buildup around the belt and pulleys increases resistance. Clean any grass or debris.
• Broken belt – Confirm the mower drive belt is not broken and in need of replacement.

Run the mower and observe the pulleys while operating. The belt should run smoothly without squealing or slipping.

Check the Carburetor

Issues with the carburetor can also lead to engine stalling. Look for:

• Dirty carburetor – Buildup of dirt and varnish in the carburetorrestricts airflow. Clean the carburetor thoroughly.
• Faulty float – The carburetor float regulates fuel intake. If stuck, fuel can flood the engine. Inspect and replace if faulty.
• Clogged jets/passages – Small blockages in jetsand passages affect the air-fuel ratio. Clean out all passages and jets.
• Sticking choke plate – If the choke plate sticks, not enough air will enter causing stall. Check that the choke moves freely.

Often just cleaning the carburetorwith some carburetor cleaner resolves many issues. Severely damaged carburetors may need rebuilding or replacing.

Check the Engine Oil Level

Another simple item to check is the engine oil level. Low engine oil can lead to lack of lubrication and engine seizure. Be sure to:

• Check oil level – Add more oil if low. Don’t overfill.
• Change oil regularly – Old, dirty oil loses its lubricating ability. Follow mower oil change intervals.
• Look for leaks – Inspect seals and gaskets for any leaks causing oil loss.

Take care to use the oil type and weight recommended by the manufacturer, usually SAE 30 or 10W30 for most mowers.

Check the Air Filter

A dirty, clogged air filter restricts air intake to the engine leading to possible stalling. Inspect and clean the filter regularly. Also:

• Check filter seating – Make sure the air filter assembly is installed correctly in the housing.
• Inspect intake piping – Ensure piping between filter and carburetor is clear and sealed.
• Check for restrictions – Make sure engine fan areas are free of clippings that block airflow.

Replace excessively dirty filtersthat are unable to be cleaned. Use manufacturer approved air filters only.

Test the Battery and Charging System

On riding mowers with electric starting systems, battery and charging issues can be a cause of hard starting. Check the following:

• Weak or dead battery – Test battery voltage. Recharge or replace battery as needed.
• Faulty starter – Starters can wear out over time. Test starter operation.
• Loose battery connections – Clean and tighten any loose battery cables.
• Charging system issues – The alternator may not be charging the battery while operating. Test charging voltage.

Refer to your mower’s service manual for the required battery voltage and charging specs. Keep batteries fully charged and free of corrosion.

Conclusion

Difficulty starting and random stalling of a riding lawn mower can be frustrating. But methodically checking each potential issue outlined above should help uncover the underlying problem. Always start with easy to check items like fuel and battery power before moving to more complex components. Refer to your equipment owner’s manual for model specific troubleshooting tips. With patience and good mechanical skills, you can get your riding mower back up and running smoothly.