There’s nothing more frustrating than getting ready to mow your lawn—only to find your mower won’t start. Whether you have a push mower, self-propelled, or riding model, there are only a handful of likely culprits. This step-by-step guide will walk you through every major reason a lawn mower won’t start, plus easy checks and solutions to get your machine running again.
Quick Picks: Most Common Reasons a Lawn Mower Won’t Start
- Old or Stale Gasoline: Gas breaks down fast and can gum up the carburetor.
- Dirty or Clogged Carburetor: Fuel residue or debris block fuel flow to the engine.
- Bad or Fouled Spark Plug: Weak or no spark means no ignition.
- Clogged Air Filter: A dirty filter restricts airflow and chokes the engine.
- Blocked Fuel Filter or Line: Dirt or debris prevents fuel from reaching the carburetor.
- Dead Battery (Electric Start/Riding Mowers): Low or dead battery means no crank or click.
- Loose or Corroded Battery Connections: Stops power from reaching the starter or ignition.
- Faulty Safety Switches: All levers, pedals, or seat switches must be engaged for the mower to start.
- Flooded Engine: Too much fuel from over-priming or a stuck choke prevents starting.
- Low or Dirty Oil: Some mowers have safety shutoffs if oil is low or old.
- Broken Pull Cord or Recoil Starter: You can’t start what you can’t spin!
- Blown Fuse or Faulty Ignition Switch: On electric start models, these can prevent starting.
Buyer’s Guide: What You’ll Need to Diagnose & Repair
- Fresh gasoline (never more than 30 days old)
- Socket wrench set for spark plug, air filter, and battery access
- New spark plug and air filter (for tune-up)
- Carburetor cleaner spray for removing gunk and varnish
- Battery charger or replacement battery
- Wire brush for cleaning spark plug or battery terminals
- Owner’s manual for location of switches and safety features
- Gloves and eye protection
Step-by-Step Guide: What to Check When Your Lawn Mower Won’t Start
1. Replace Old Gas and Clean the Carburetor
- Drain old fuel from the tank and carburetor bowl (if accessible).
- Refill with fresh, clean gasoline.
- Spray carburetor cleaner into the carb intake—especially if the mower sat unused for months.
2. Inspect and Replace the Spark Plug
- Remove the spark plug with a socket wrench.
- Clean the tip with a wire brush, or replace if it’s worn, cracked, or blackened.
- Ensure the wire snaps on tightly when reinstalled.
3. Check and Replace the Air Filter
- Remove the filter cover and inspect the air filter for dirt, oil, or clogging.
- Replace with a new filter if it’s dirty—this is one of the simplest, most effective fixes.
4. Inspect Fuel Lines and Filter
- Check all lines for kinks, cracks, or blockages.
- Replace the fuel filter if you see dirt, discoloration, or slow flow.
5. Test and Charge or Replace the Battery (If Equipped)
- Measure battery voltage with a multimeter—should be 12.4–12.8V for 12V systems.
- Charge if low; replace if it won’t hold a charge after a full cycle.
- Clean all connections with a wire brush before reattaching.
6. Check Safety Switches and Controls
- Ensure all levers, brake pedals, seat switches, and blade controls are set for starting.
- Test switches for clicking or proper movement—replace any that are loose or broken.
7. Avoid a Flooded Engine
- If you smell strong gas or see a wet plug after repeated starting attempts, let the mower sit 15–30 minutes.
- Try starting again with the choke off and the throttle open.
8. Inspect Oil Level and Quality
- Low or dirty oil can trigger a safety shutoff on some models.
- Check and add oil if needed, or change oil if it’s dark, thick, or gritty.
9. Examine Pull Cord and Starter Mechanism
- If the pull cord is stuck, frayed, or won’t retract, inspect and repair the recoil starter.
- Replace the cord if it’s worn or broken.
10. Check Fuses and Ignition Switch (Electric Start)
- Find the fuse near the battery or ignition—replace if blown.
- If turning the key produces nothing, test or replace the ignition switch.
Comparison Table: Lawn Mower Starting Problems & Solutions
| Problem | Solution | Difficulty | Parts Needed |
|---|---|---|---|
| Old/Stale Gas | Drain and replace fuel | Easy | Fresh gasoline |
| Dirty Carburetor | Clean with spray or rebuild | Easy-Medium | Carb cleaner, gaskets |
| Bad Spark Plug | Clean or replace plug | Easy | Spark plug |
| Clogged Air Filter | Replace filter | Easy | Air filter |
| Blocked Fuel Line/Filter | Replace line or filter | Easy | Fuel filter/line |
| Dead Battery | Charge or replace | Easy | Battery, charger |
| Loose/Corroded Connections | Clean and tighten connections | Easy | Wire brush |
| Faulty Safety Switch | Replace switch | Easy | Switch, wiring |
| Flooded Engine | Wait, start with choke off | Easy | — |
| Low/Dirty Oil | Add/change oil | Easy | Oil |
| Broken Pull Cord | Replace pull cord | Easy-Medium | Starter rope |
| Blown Fuse/Ignition Switch | Replace fuse or switch | Easy | Fuse, switch |
Frequently Asked Questions
Why does my mower click but not start?
This usually points to a weak battery, loose cable, or faulty starter solenoid (on electric models). Charge/replace the battery and check connections.
How often should I tune up my mower?
Change the spark plug and air filter at least once per mowing season for easy starts and reliable running.
What’s the easiest way to prevent starting problems?
Use fresh gas, perform regular tune-ups, and store your mower properly over the winter. Clean or replace filters and plugs each season.
When should I seek professional help?
If you’ve checked everything here and your mower still won’t start, it may be time for a small engine mechanic to check deeper engine or electrical problems.
Conclusion
A mower that won’t start is almost always caused by bad fuel, a dirty carburetor, fouled plug, or a clogged filter. Go step by step, and you’ll almost always find the cause—and get your lawn looking sharp again in no time!