When your lawn mower refuses to “fire”—meaning it cranks but doesn’t even try to start, or maybe just coughs once and dies—the problem usually comes down to spark, fuel, or air. But the ignition system is often the main culprit, especially if your engine seems completely dead. Whether you have a push mower, self-propelled, or riding model, this comprehensive guide will walk you through every cause and solution for a lawn mower that won’t fire, so you can get back to mowing with confidence.
Quick-Check: Why Isn’t My Lawn Mower Firing?
- No spark at the plug (bad spark plug, ignition coil, or kill switch)
- Fouled, wet, or damaged spark plug
- Disconnected, loose, or corroded spark plug wire
- Faulty ignition coil or armature
- Bad safety switch (handle, seat, brake, or blade)
- Engine kill switch stuck or damaged
- Carburetor flooding or not delivering fuel (if engine “pops” but won’t run)
- Clogged air filter (rarely stops firing, but can make starting hard)
- Flywheel key sheared (often after striking a hard object)
- Dead battery (electric start mowers) or wiring problems
- Internal engine problems (low compression, rarely the cause unless the engine is old or damaged)
1. Check for Spark: The Most Common Reason for No Firing
- Remove the spark plug from the engine using a spark plug wrench.
- Reconnect the spark plug wire and ground the metal plug body against the engine block (away from the plug hole).
- Crank the engine—look for a blue or strong spark at the plug tip. No spark means an ignition issue.
- If you see only a weak, orange, or no spark at all, continue with the next steps.
2. Inspect and Replace the Spark Plug
- Check for black soot, wetness (gas or oil), cracks, rust, or damaged electrodes.
- Clean a lightly fouled plug with a wire brush. Replace if it’s badly fouled, worn, or damaged.
- Set the spark plug gap per your mower’s manual (usually 0.028–0.030 inches).
- Always use the correct spark plug type for your mower engine.
3. Test the Spark Plug Wire and Connection
- Inspect the wire for cracks, cuts, or corrosion on the terminal.
- Ensure the boot fits tightly on the spark plug.
- Replace the wire if it feels loose, damaged, or won’t stay connected.
4. Check the Ignition Coil (Armature)
- If you have no spark with a good plug and wire, the ignition coil may be faulty.
- Most coils are easy to access—just remove the engine cover (shroud).
- Inspect for rust, corrosion, or broken wires at the coil or kill wire connection.
- If possible, test coil resistance with a multimeter (refer to your manual for specs).
- Replace the coil if it’s out of spec or still no spark with all other parts replaced.
5. Inspect Kill Switches and Safety Features
- Most mowers have a kill switch or “deadman” lever that grounds the ignition to stop the engine.
- Check the kill wire (usually a thin wire running from the coil to the switch or handle). Disconnect this wire at the coil—if you get spark now, the switch or wire is bad.
- Test all safety switches: seat (riding), handle lever, brake/clutch, blade control. If any are faulty, the ignition is grounded and won’t spark.
- Replace or repair bad switches and damaged wires.
6. Check for a Sheared Flywheel Key
- If your mower hit a rock or other hard object, the flywheel key may shear—throwing ignition timing off and causing no spark or backfiring.
- Remove the flywheel and inspect the key. Replace if damaged (cheap and easy fix).
7. Battery, Starter, and Electrical (For Electric Start or Cordless Mowers)
- Check that the battery is fully charged and cables are clean and tight.
- Check main fuses, relays, and switches—replace as needed.
- On battery mowers, ensure all safety keys, handles, and controls are properly engaged before starting.
8. Air and Fuel: If It Fires But Won’t Run
- If you have spark but the engine only “pops” or coughs, you may have a fuel or air problem.
- Check for old/stale gas, clogged carburetor jets, or a dirty air filter.
- Clean the air filter or try starting briefly without it (replace before regular use).
- If the plug is wet with gas, the engine may be flooded—remove the plug, let dry, and try again after clearing excess fuel.
Preventive Maintenance: Avoid No-Fire Issues
- Replace the spark plug every spring or after 25 hours of use
- Keep the ignition coil, wires, and kill switches clean and dry
- Inspect and repair wiring and safety switches regularly
- Clean under the engine shroud to prevent overheating and corrosion
- Use fresh fuel and keep air filter clean for strong, consistent firing
Frequently Asked Questions (FAQ)
How do I know if my mower is getting spark?
Remove the plug, ground it to the engine, and crank. A visible blue spark at the electrode means the ignition is working.
Can a bad spark plug cause no firing?
Yes—a fouled, damaged, or wrong-gap spark plug is the top cause of no firing. Replace with a new, correct plug.
Why does my mower fire once then die?
This usually means it’s getting a quick burst of fuel and spark, but either one or both are interrupted—often a kill switch, carb issue, or bad coil.
Is it safe to bypass safety switches?
Only for brief troubleshooting. Never operate your mower with safety switches disabled—replace or repair them promptly.
When should I call a repair shop?
If you have no spark after replacing the plug, checking the coil and wires, and testing safety switches, or if you suspect internal engine damage, it’s time for professional help.
Conclusion: Restore Spark and Fire Up Your Mower
A mower that won’t fire is almost always the result of a spark issue—bad plug, coil, safety switch, or kill wire. With these troubleshooting steps, you can quickly identify and fix most problems at home. Stay on top of regular maintenance, and your mower will start easily and run reliably all season long. If you run into persistent issues, your local small engine shop can help you get back to a healthy, beautiful lawn.
Ready for a quick fix? Restore the spark and fire up your mower with confidence!