You’re ready to get your lawn in shape, but your mower simply refuses to start. This is a classic frustration for homeowners and gardeners everywhere. Whether you use a push mower, riding mower, or even a battery-powered machine, a non-starting lawn mower can stop your yard work in its tracks. The good news? Most issues are easy to identify and fix once you know what to look for. This guide covers all the major reasons a lawn mower won’t start—and how to get it running again.
1. Common Reasons Your Lawn Mower Won’t Start
- Old or stale gasoline in the tank
- Dirty or faulty spark plug
- Clogged or dirty air filter
- Battery problems (for electric start mowers)
- Carburetor issues
- Faulty safety switches or wiring
- Obstructions under the mower deck
- Low or dirty oil
2. Quick-Check: The Simple Things to Rule Out First
- Fuel: Is there fresh gas in the tank? If it’s more than 1–2 months old, drain it and refill with new gasoline.
- Oil: Check the dipstick. Add oil or change it if needed. Many modern mowers won’t start with low or dirty oil.
- Spark Plug: Make sure the plug wire is securely attached. Remove and inspect the plug—it should be clean and undamaged.
- Air Filter: Remove and check your air filter. Clean or replace it if it’s dark, oily, or clogged.
- Safety Levers/Switches: Squeeze all necessary handles, sit in the seat (for riding mowers), and ensure the brake is engaged.
- Battery: On electric start mowers, check the battery’s charge and clean the terminals.
3. Fuel System Troubles: Gas, Carburetor, and Filters
Most starting problems come down to the fuel system. Here’s what you need to check:
- Stale or old gas: Gasoline breaks down quickly and can gum up your engine. Always use fresh fuel and consider adding a stabilizer if you store your mower for long periods.
- Blocked fuel filter: Inspect and replace the fuel filter if it’s dirty or clogged.
- Dirty carburetor: If old gas sits in the carburetor, it can gum up the tiny passages. Spray carburetor cleaner into the air intake, or remove and clean the carburetor for best results.
- Check the fuel shutoff valve: If your mower has one, make sure it’s open.
- Look for water in the fuel tank: Water separates from gas and will not burn. Drain and refill if you see cloudy fuel or droplets at the bottom of the tank.
4. Ignition and Spark Plug Issues
No spark means no start! The spark plug is a small part, but it plays a big role.
- Remove and inspect the spark plug. Look for carbon buildup, oil fouling, or damage.
- Clean the plug with a wire brush, or replace it if it’s in bad shape. Spark plugs are cheap and easy to swap.
- Check the spark plug gap using a gap tool and adjust to spec.
- Test for spark: Attach the plug wire, touch the plug’s threads to the engine block, and crank the engine. A blue spark should jump the gap.
- If there’s no spark, the issue could be the ignition coil or wiring.
5. Air Intake and Air Filter Problems
Your engine needs clean air for combustion. A blocked air filter starves the engine, making it hard or impossible to start.
- Check the air filter. If it’s covered in dust, grass, or oil, clean or replace it.
- Try running the engine briefly without the filter (for a test only). If it starts, replace the filter with a new one.
- Clean foam filters with warm, soapy water, dry fully, and reinstall.
- Replace paper filters if they’re discolored or blocked.
6. Battery and Electrical Issues (Electric Start & Riding Mowers)
If your mower clicks, turns slowly, or shows no signs of life with the key, suspect a battery or electrical issue.
- Check battery voltage with a multimeter. A healthy battery should read at least 12.4 volts.
- Clean the battery terminals. Remove corrosion with a wire brush.
- Charge or replace the battery if it’s weak or old.
- Check for blown fuses or loose wires near the starter or ignition switch.
- Listen for clicking sounds. A click but no crank usually points to a bad solenoid or starter.
7. Mechanical Issues: Blade or Engine Obstruction
Sometimes the engine won’t crank or feels locked up. Here’s what to check:
- Disconnect the spark plug wire for safety.
- Check under the mower deck for obstructions. Clear any sticks, rocks, or grass clumps blocking the blade.
- Try spinning the blade by hand (with gloves). It should move freely. If not, the engine might be seized or jammed.
- Check the oil level. Low oil can cause some mowers to seize up or trigger safety shutoffs.
8. Safety Switches and Controls
Modern mowers are full of safety features. If any switch is not engaged, your mower won’t start.
- Blade control lever or presence bar: Must be held down to start.
- Seat switch (riding mowers): Must be pressed by your weight.
- Parking brake: Must be engaged.
- Inspect switch wiring for visible damage or looseness.
- Replace or repair faulty switches as needed.
9. Carburetor and Fuel Delivery Problems
The carburetor mixes air and fuel for combustion. If it’s dirty or blocked, your mower may crank but not start.
- Spray carburetor cleaner into the air intake. If the engine fires briefly, it’s likely a carburetor issue.
- Remove and clean the carburetor if you’re comfortable, or take it to a small engine repair shop.
- Check for cracked or leaking fuel lines and replace as necessary.
10. Flooded Engine
- If you smell strong gas or the spark plug is wet, let the mower sit for 10–15 minutes to clear excess fuel.
- Pull the cord a few times with the plug out to clear the cylinder, then dry and reinstall the plug.
- Try starting again with no choke.
11. When to Call a Professional
If you’ve checked all these steps and your mower still refuses to start, the problem may be more serious. Worn-out piston rings, low compression, or advanced electrical issues usually require help from a small engine repair specialist.
12. Preventive Maintenance: Keep Your Mower Running Strong
- Use fresh gasoline, and drain old gas before winter storage.
- Change the oil, spark plug, and air filter at least once per season.
- Clean under the deck after every mow to prevent clogs.
- Store your mower in a dry, sheltered area.
- Check and charge the battery over the winter (if equipped).
13. Frequently Asked Questions (FAQ)
Why does my mower crank but not start?
Usually, the issue is with fuel, spark, or air—most commonly old gas, a bad spark plug, or a dirty air filter.
How do I know if my spark plug is bad?
Look for black, sooty buildup, rust, or a cracked electrode. Replace the plug if in doubt—it’s a cheap fix that solves many problems.
Can a dirty carburetor cause a no-start?
Absolutely. A gummed-up carburetor is a common culprit when a mower turns over but won’t fire up. Clean or rebuild the carb if needed.
How often should I change my air filter?
At least once per mowing season, or more often if you mow a large yard or in dusty conditions.
Is it worth repairing an old mower that won’t start?
If the engine is in good shape and the deck isn’t rusted through, most repairs are inexpensive. For very old or heavily-used mowers, it may be time to consider a replacement.
14. Conclusion: Get Back to Mowing with Confidence
A non-starting lawn mower can put a real damper on your day, but most problems have simple, affordable fixes. Start with the basics—fuel, spark, air, and battery—and work through the troubleshooting steps above. With a little patience and regular care, you’ll have your mower running smoothly and your yard looking great all season long.
Still stuck? Local small engine repair shops can diagnose and repair even the toughest mower problems, so you can get back to what matters—enjoying your yard!