You turn the key or pull the cord and…nothing. Or maybe the engine cranks but refuses to start.
A lawn mower that won’t start can have a surprisingly simple cause, but finding it usually means working through a few possibilities. Before replacing parts, start with the basics and narrow down the problem.
Whether you have a riding mower, zero-turn mower or walk-behind mower, here are 10 common areas worth checking.
1. Old or Contaminated Fuel
Fuel is one of the easiest places to start.
Gasoline that has been sitting for an extended period can deteriorate and create starting problems. Moisture or debris in the fuel can cause trouble as well.
If your mower has been sitting unused, check the condition of the fuel before moving on to more complicated possibilities.
2. Clogged Fuel Filter
A clogged lawn mower fuel filter can restrict the amount of fuel reaching the engine.
Inspect the filter for visible contamination and check the recommended replacement interval for your mower. If you're replacing it, make sure the new filter matches the correct application and fuel-flow direction.
3. Dirty Air Filter
An engine needs the right mixture of fuel and air to run properly.
A heavily clogged lawn mower air filter can restrict airflow and contribute to hard starting, rough operation or poor engine performance.
Foam and paper filters require different maintenance, so follow the recommendations for your particular engine.
4. Worn or Fouled Spark Plug
The spark plug is another common place to look when a lawn mower cranks but won't start.
Remove the plug and inspect its condition. Heavy carbon buildup, damage or excessive wear may indicate that replacement is due.
Before purchasing a new spark plug, verify the correct part number and gap specification for your engine.
5. Ignition Coil Problems
If the engine isn't producing the spark it needs, the ignition system may require further inspection.
The ignition coil helps provide voltage to the spark plug. A damaged coil, connection problem or incorrect air gap can potentially cause a no-start condition.
Because several issues can produce similar symptoms, test and inspect the ignition system before assuming the coil itself needs replacement.
6. Carburetor Problems
When a mower has been sitting for a while, the carburetor often gets blamed—and sometimes for good reason.
Old fuel and deposits can interfere with small passages inside the carburetor and affect fuel delivery.
Symptoms can include an engine that won't start, starts and quickly dies, only runs with the choke on or runs poorly.
Cleaning may solve some carburetor problems. In other situations, a replacement lawn mower carburetor or rebuild components may be needed.
7. Fuel Pump Issues
Many riding mowers and zero-turn mowers use a fuel pump to move gasoline from the tank to the carburetor.
If you're not getting adequate fuel delivery, inspect the entire system rather than immediately replacing the pump. Check the fuel lines, filter, connections and other related components for restrictions, leaks or damage.
8. Weak Battery or Poor Connections
If your riding lawn mower won't start or turns over slowly, check the battery and electrical connections.
A discharged battery, loose terminal or corroded connection can prevent the starter from receiving the power it needs.
Don't judge the battery only by whether the lights work. Starting the engine requires considerably more current.
9. Starter Solenoid or Starter Problems
If you turn the key and hear a click but the engine doesn't crank, the starting circuit deserves a closer look.
Depending on the mower, possible areas include the battery, cables, starter solenoid, starter motor, ignition switch and electrical connections.
A clicking sound alone isn't enough to confirm that the starter solenoid is bad, so testing can help avoid replacing a good part.
10. Safety Switches and Interlocks
Modern riding mowers and zero-turns typically use several safety switches.
Depending on the machine, the mower may need the brake engaged, PTO disengaged, operator in the seat or steering controls in a particular position before it will start.
If everything else appears normal, a damaged switch, loose connector or issue with the safety interlock system may be worth investigating. Never bypass a safety device to get the mower running.
Find the Right Replacement Lawn Mower Parts
The biggest mistake when troubleshooting a mower is replacing parts based only on a symptom.
A mower that won't start doesn't automatically need a carburetor, starter or ignition coil. Take a few minutes to determine whether you're dealing with a fuel, air, spark or electrical problem first.
Once you've narrowed down the problem, use your mower's model number, engine model and OEM part number to identify the correct replacement.
Reliable Aftermarket Parts carries aftermarket lawn mower parts for a wide range of riding mowers, zero-turn mowers and outdoor power equipment. Our selection includes filters, carburetors, ignition components, starters, solenoids, fuel system parts, belts, blades, spindles and more.
When it's time to replace a worn component, having the OEM number and equipment information ready can make finding the right part considerably easier.