When your lawn mower refuses to start, one of the most common culprits is a lack of spark at the spark plug. No spark means the engine can’t ignite the air-fuel mixture—so you’re left with endless pulling, frustration, and no results. The good news? Most spark problems can be diagnosed and fixed at home with simple tools and a step-by-step approach. Here’s everything you need to know to get your lawn mower firing up again.
Quick Picks: Common Reasons Your Lawn Mower Isn’t Getting Spark
- Faulty Spark Plug: The plug itself is damaged, fouled, or worn out.
- Disconnected or Loose Plug Wire: The boot isn’t firmly attached or wire is damaged.
- Bad Ignition Coil: The coil no longer sends voltage to the spark plug.
- Faulty Safety Switches: Many mowers have kill switches or safety levers that ground the coil and stop spark.
- Broken or Disconnected Kill Switch Wire: If this wire is grounding the coil, you’ll get no spark.
- Flywheel Key Sheared: On rare occasions, a sheared key can throw timing and kill spark.
- Corroded Electrical Connections: Rust or moisture can interrupt current flow.
Buyer’s Guide: What You Need to Test and Fix Spark Issues
- New spark plug: Always keep a spare, correct type for your model.
- Spark tester: A simple, inexpensive tool for checking spark visually.
- Socket wrench & screwdriver set: For plug, shroud, and coil access.
- Multimeter: For continuity checks (optional).
- Fine sandpaper or wire brush: For cleaning plug contacts.
- Replacement ignition coil or module: If needed for repair.
- Service manual or online diagram: To help locate parts and wiring.
- Work gloves and eye protection: For safety during repairs.
Step-by-Step: How to Fix a Lawn Mower With No Spark
1. Remove and Inspect the Spark Plug
- Disconnect the spark plug boot and remove the plug with a socket.
- Check for black carbon deposits, cracks, or a fouled tip.
- Clean the plug with sandpaper or a wire brush, or replace if damaged or heavily fouled.
- Reinstall and retest for spark.
2. Test for Spark Using a Spark Tester
- Attach the tester between the spark plug wire and the plug.
- Crank or pull the mower. You should see a visible spark in the tester window.
- No spark? Move on to the next step.
3. Check Spark Plug Wire and Boot
- Ensure the plug wire is firmly attached at both ends—at the spark plug and the ignition coil/module.
- Look for cracks, corrosion, or breaks in the wire or boot.
- Replace the wire if damaged or excessively worn.
4. Inspect Safety and Kill Switches
- Most modern mowers have a kill switch, bail bar, or safety lever that must be engaged for spark.
- Check that all levers and switches are working and that wires are not loose, broken, or grounding out the coil unintentionally.
- Disconnect the kill switch wire from the coil and test for spark again—if you now get spark, the switch or wiring is at fault.
5. Test the Ignition Coil
- With all switches in working order and still no spark, the ignition coil is the likely culprit.
- Remove the blower housing to access the coil.
- Check for rust, cracks, or signs of arcing. Use a multimeter for continuity, or simply swap in a new coil to test.
- Replace the coil if defective, ensuring the correct air gap to the flywheel (usually around 0.010–0.014 inches—check your manual).
6. Inspect the Flywheel Key (if needed)
- If your mower hit a rock or hard object before spark was lost, the flywheel key may be sheared, throwing off timing and disabling spark.
- Remove the flywheel to inspect and replace the key if needed.
Comparison Table: Lawn Mower No Spark Causes & Solutions
| Problem | Solution | Difficulty | Parts Needed |
|---|---|---|---|
| Bad Spark Plug | Clean or replace plug | Easy | Spark plug |
| Loose/Bad Plug Wire | Reconnect or replace wire/boot | Easy | Wire/boot |
| Faulty Ignition Coil | Replace coil/module | Medium | Ignition coil |
| Defective Kill Switch | Repair or replace switch/wire | Easy | Switch, wire |
| Sheared Flywheel Key | Replace key | Medium | Flywheel key |
| Corroded Connections | Clean and tighten all contacts | Easy | Sandpaper, cleaner |
Frequently Asked Questions
How do I know if my mower’s coil is bad?
If you have a new plug, working wire, and no spark with all safety switches engaged, the coil is usually to blame. Replace the coil if in doubt.
Why does my mower only spark sometimes?
Intermittent spark usually means a failing coil or a loose/broken wire. Heat can also cause weak or lost spark as coils fail.
Can I bypass safety switches to test for spark?
Yes—temporarily disconnect the kill switch wire at the coil for testing. Never run the mower with safety features bypassed for regular use.
How often should I replace my spark plug?
Once per season is best, or sooner if the engine misfires, stalls, or starts hard.
What regular maintenance prevents spark problems?
- Replace spark plug yearly.
- Inspect and clean wires and terminals.
- Keep mower dry and stored out of rain/moisture.
- Don’t kink or pull plug wires roughly during maintenance.
Conclusion
No spark doesn’t have to mean a new mower or an expensive repair. With a simple, step-by-step process, you can track down and fix the most common spark issues—whether it’s a bad plug, faulty coil, or a problem with safety switches or wires. Regular tune-ups and basic checks will keep your mower running strong for years to come—and help you avoid spark problems next mowing season.