Troubleshooting Guide for Lawn Mowers Won't Start

A beautiful lawn is every homeowner's pride, and your trusty lawn mower is essential to its upkeep. But when your lawn mower won't start, it can be frustrating; common causes range from maintenance oversights to engine malfunctions. In this comprehensive guide, we explore these causes while offering step-by-step troubleshooting strategies to get it running again as soon as possible.

Lawn Mower Won't Start Initial Troubleshooting

Before diving deeper, let's perform some preliminary checks:

Safety First: Always put safety first when working on the mower or conducting inspections or repairs on its engine. Ensure it has been switched off, the spark plug wire has been disconnected, and the engine has cooled before performing repairs or inspections.

Fuel Level: Verify whether there is sufficient gasoline in the tank; running out of gas is often one of the primary reasons a mower doesn't start up properly.

Fuel Quality: Old or contaminated gasoline may lead to vehicle starting issues. If it has been sitting in your tank for an extended period, drain it and replace it with fresh gasoline as soon as possible.

Spark Plug Inspection: Inspect your spark plug to check for signs of wear, damage, or fouling that could prevent proper ignition of your vehicle. A worn or fouled spark plug could fail to produce enough of a spark required for ignition; in such an instance, it should be replaced immediately with one in good condition.

Air Filter: If the engine requires air for proper function, a dirty or clogged air filter could reduce airflow to it and affect its performance, restricting performance significantly. Therefore, it's essential that we regularly check, clean, or replace as necessary if this part needs attention.

Safety Interlock Switches: Some mowers contain safety features like seat and blade engagement switches that must work perfectly to function safely. Otherwise, it could prevent the starting of your machine due to safety concerns. Ensure these features are working efficiently, as failure to do so may stop its engine from starting in an emergency scenario.

Ignition System Issues

If preliminary checks don't resolve your mower starting issues, the ignition system could likely be to blame; such issues often make non-starters unusable.

Check Spark Plug: Remove the spark plug using a spark plug socket, inspect for wear, fouling, or damage, and replace if necessary based on manufacturer specs (if one exists). Finally, ensure it's gapped according to mower specs for best performance.

Inspect the Spark Plug Wires: Ensure the wires connecting each spark plug to the ignition system are secure and undamaged; replace as necessary if required.

Test for Spark: To check whether or not the ignition system is producing a spark, follow these steps:

Reconnect the spark plug wire to its spark plug. Securing its metal body to an engine block or another metal surface. Crank your engine (pull the starter cord). Check for the visible spark between a spark plug electrode and metal surface; this indicates if your ignition system is functioning normally; otherwise, there could be issues with its coil, magneto, or other ignition components.

Fuel System Problems

If the mower still won't start after applying the spark, but the spark is present, then perhaps your fuel system needs adjustment.

Check Fuel Lines: Inspect fuel lines for cracks, leaks, or blockages and replace any damaged or clogged lines immediately.

Clean Your Carburetor: To maintain optimal operation of a carburetor system. Clogged or dirty carburetors prevent fuel from reaching your engine. To clean one on your mower, follow these steps:

Locate and isolate the carburetor on your lawn mower (it can often be found under or near the air filter or engine). Take steps to remove its cover or air filter housing before opening up its cover again to complete its task of clearing.

Clean the interior components using carburetor cleaner spray, including jet, float bowl, and throttle plate. Reassemble the carburetor and air filter housing after use. 

Engine Compression Issues

Low engine compression may prevent your mower from starting. To check it:

Compression Test: Remove the spark plug. Insert a compression tester into its respective spark plug hole. Crank your engine several times while monitoring compression readings to indicate engine health.

Check Your Mower Manual: To determine the appropriate compression range for your mower.

If it drops too low, this could indicate issues with piston rings, valves, or the cylinder head gasket. In this case, professional services should be sought from an experienced mechanic. 5 Other Considerations

If, after going through these steps, your mower won't start, consider these factors.

Oil Level: Some mowers feature an auto low-oil shutdown feature, which prevents the starting of their engines when oil levels fall too low; make sure you check this and add any necessary amounts as soon as you detect low levels.

Choke Position: Before beginning your mower's engine, ensure the choke lever or knob is in an ideal starting position. Consult your manual for guidance in using it effectively.

If your mower offers electric start capabilities, inspect its battery's charge and connections regularly - weak or dead batteries could prevent its effectiveness and, therefore, stop working as intended.

Fuel Quality: Poor-grade or contaminated gasoline may contribute to starting issues, so ensure you're using fresh gasoline that has not become polluted over time.

Exhaust System: Clogs or obstructions in an exhaust system may impair engine performance; check both pipes and muffler for blockages to assess possible performance issues.

If all troubleshooting steps have failed to resolve your lawn mower problems and it still won't start up, professional assistance might be required to fix the issue. Issues related to internal engine components or major electrical faults might warrant expert intervention from certified technicians.


An inoperable lawn mower termed “lawn mower won't start” can be an unexpected obstacle in your lawn care routine, but systematic troubleshooting can identify and fix issues quickly. By inspecting ignition system components such as the ignition coil, fuel system components, compression ratio, and other critical parts, you may identify the source of your non-start before taking appropriate action to address it. Regularly maintaining and tuning up your mower will also help avoid such problems from occurring in the first place - taking this approach will have your mower running like new in no time and your lawn looking its finest, too!

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