There’s nothing more frustrating than dragging your lawn mower out on a sunny afternoon, only to find that it just won’t start. This problem is incredibly common, whether you’re using a push mower, self-propelled model, or riding mower. Fortunately, most starting issues have simple causes—and many can be fixed with just a little time and know-how. This comprehensive guide will help you identify the reasons your lawn mower isn’t starting and walk you through solutions step-by-step.
Quick Summary: Top Reasons Lawnmowers Won’t Start
- Old or stale gasoline
- Dirty or faulty spark plug
- Clogged air filter
- Battery issues (for electric start mowers)
- Clogged carburetor
- Disconnected safety switches
- Obstructions under the mower deck
1. Initial Checks: Don’t Overlook the Basics
Before digging into more complex problems, take a moment to inspect the simple things. Many mower starting problems come down to a quick fix.
- Is there fuel in the tank? Double-check that the gas tank isn’t empty.
- Is the fuel fresh? Gasoline can go bad after just a month or two, especially if your mower sat unused over the winter.
- Is the oil level correct? Check the dipstick and top up if necessary. Low or dirty oil can trigger safety switches that prevent starting.
- Is the spark plug wire attached? Make sure the spark plug boot is pushed on tightly.
- Is the air filter clean? Remove and check the filter for heavy dirt, dust, or oil. Clean or replace as needed.
- Are all safety handles and levers fully engaged? Most mowers won’t start unless the blade control bar is held down or, for riding mowers, unless you’re seated and the brake is engaged.
2. Fuel System Problems
Gasoline is the lifeblood of your mower’s engine. If the fuel system isn’t working correctly, your mower won’t start, or it may run roughly and stall out. Here’s what to check:
- Stale or old fuel: Drain any gas that’s more than 1–2 months old and refill with fresh gasoline.
- Blocked fuel filter or fuel line: Look for any kinks, blockages, or leaks. Replace filters that appear clogged or dirty.
- Dirty carburetor: The carburetor can become gummed up, especially if old fuel sat in the system. Use a carburetor cleaner spray, or remove and clean the carb thoroughly.
- Fuel shutoff valve closed: If your mower has one, make sure it’s open.
3. Spark Plug and Ignition Issues
No spark, no start. The spark plug delivers the electric jolt that ignites the fuel in the engine. If it’s fouled, damaged, or disconnected, your mower will never fire up.
- Remove and inspect the spark plug. Look for black carbon, oil residue, rust, or a cracked porcelain insulator.
- Clean the plug with a wire brush, or replace it if in doubt. Spark plugs are inexpensive and easy to change.
- Check the spark plug gap. If it’s set incorrectly, adjust it to the manufacturer’s specs.
- Test for spark: Reconnect the wire, hold the plug’s metal body against the engine block, and pull the starter cord. You should see a strong blue spark. If not, try a new plug or check the ignition coil.
4. Air Filter Blockages
Lawnmower engines require the right mixture of air and fuel to run. A dirty air filter chokes off airflow, making starting difficult or impossible.
- Remove the air filter cover and inspect the filter.
- Clean foam filters with soap and water. Let them dry fully before reinstalling.
- Replace paper filters if they’re dirty or clogged.
- Try starting the mower with the filter removed (just for a test). If it starts, replace the air filter.
5. Battery and Electrical Issues (For Electric Start Models)
If your mower has an electric starter, a weak or dead battery is a common reason for a no-start. Here’s what to do:
- Check battery terminals for corrosion. Clean if needed, and tighten any loose connections.
- Test the battery voltage with a multimeter. Most mower batteries should show at least 12.4 volts when fully charged.
- Charge the battery if it’s low, or replace it if it’s several years old.
- Listen for a click when turning the key. If you hear nothing, the battery, starter solenoid, or ignition switch could be faulty.
6. Carburetor Problems
The carburetor mixes air and fuel for combustion. If it’s dirty or clogged, your mower will struggle to start—or won’t run at all.
- Spray carburetor cleaner into the air intake and try starting the mower. If it fires briefly, the carb likely needs a deeper cleaning.
- Remove the carburetor if you’re comfortable, and clean out all jets and passages.
- Reinstall carefully, making sure gaskets and seals are in good shape.
- If you’re not comfortable cleaning it yourself, take your mower to a professional.
7. Safety Switches and Controls
Nearly all modern lawnmowers are equipped with safety switches that prevent starting unless certain conditions are met. Here’s what to check:
- Blade control bar or handle must be fully engaged.
- Seat switch (for riding mowers): Must be occupied.
- Parking brake (riding mowers): Must be engaged.
- Inspect safety switch wiring for visible damage.
- Wiggle levers and handles to ensure they’re not stuck or jammed.
8. Mechanical Obstructions and Deck Problems
Sometimes, a simple blockage can keep your mower from turning over or running properly.
- Always disconnect the spark plug wire before looking under the mower.
- Check for sticks, rocks, or built-up grass clippings jamming the blade or deck.
- Remove any obstructions before attempting to start the mower again.
9. Flooded Engine? Here’s What to Do
Pulling the starter cord too many times (especially with the choke on) can flood the engine with fuel. If you smell strong gas or see a soaked spark plug, let the mower sit for 10–15 minutes to evaporate excess fuel, then try starting with the choke off and throttle open.
10. Less Common (But Serious) Issues
- Broken flywheel key: If you hit something hard, the flywheel key can shear, throwing off engine timing.
- Bad ignition coil: If you have no spark with a new plug, the coil could be bad.
- Compression problems: Worn rings or valves mean the engine won’t build enough pressure to start.
- Starter solenoid or switch failure (electric start): No click or crank when you turn the key.
For these, professional service is often your best bet.
11. Prevent Future Starting Problems: Essential Maintenance Tips
- Drain old fuel or use a fuel stabilizer if storing the mower for more than a month.
- Change the oil and spark plug at the start of each mowing season.
- Keep the air filter clean and replace it yearly.
- Clear grass and debris from the deck after every use.
- Store your mower in a dry place, away from rain or moisture.
12. Frequently Asked Questions (FAQ)
What should I check first when my lawn mower won’t start?
Always start by checking for fresh fuel, a clean air filter, a good spark plug, and properly engaged safety switches.
Can old gasoline cause my mower not to start?
Absolutely. Old gas can gum up the carburetor and prevent proper combustion. Always use fresh gas.
What if my mower starts, then quickly stalls?
This usually points to a dirty carburetor or a blocked air filter. Clean both and try again.
Is it safe to tip my mower to look underneath?
Yes, but always disconnect the spark plug wire first. Tip with the air filter side up to avoid oil leaks.
When should I call a professional?
If you’ve tried the steps above and the mower still won’t start—or if you suspect internal engine damage or electrical failure—a professional can diagnose and repair more complex problems.
13. Conclusion: Don’t Let a Stubborn Mower Stop You
Most lawn mower starting problems are caused by easy-to-fix issues like bad gas, dirty filters, or a worn spark plug. With a methodical approach and regular maintenance, you can solve the vast majority of problems yourself and keep your yard looking sharp all season long. If the problem is more serious, don’t hesitate to contact a local small engine repair shop—sometimes a professional touch is the best way to get back on track.
Ready to get mowing again? Start with these steps and you’ll likely have your lawn mower purring in no time.