You go to start your lawn mower for the first cut of the season, and nothing happens. It’s a frustrating situation every homeowner faces. If you’re wondering why wont my lawn mower start, you’re not alone. Several frequent issues, from stale fuel to a faulty spark plug, can prevent a mower from starting. This guide will walk you through the most common causes and their fixes, in a logical order, so you can get back to mowing quickly.
Why Wont My Lawn Mower Start
Before you call for expensive repair service, you can diagnose most problems yourself. The key is to follow a systematic approach. Start with the simplest, most common solutions and work your way toward the more complex ones. Always remember to disconnect the spark plug wire before performing any maintenance to ensure your safety.
Check The Obvious First
It sounds silly, but often the solution is right in front of you. Overlooking a simple step can waste a lot of time and effort. Always eliminate these basic possibilities before moving on to mechanical troubleshooting.
Fuel Shutoff Valve And Choke
Many lawn mowers have a small fuel valve on the line between the gas tank and the carburetor. If this valve is closed, no fuel can reach the engine. Make sure it’s in the “On” position. Also, check the choke setting. A cold engine requires the choke to be closed (or on) to start. If the engine is warm or the choke is stuck open, it may not start.
Blade Engagement And Safety Levers
Your mower is designed with safety interlocks. If the blade engagement lever is pulled, the engine may not crank. Ensure the blade is disengaged. Also, on many walk-behind mowers, you must hold a safety lever on the handle down for the engine to start or run. Check that this lever is functioning properly.
Problem 1: Bad Or Stale Gasoline
This is the single most common reason a lawn mower won’t start, especially after winter storage. Gasoline begins to degrade in as little as 30 days. Over months, it forms varnish and gum that clogs the carburetor’s tiny fuel passages.
- Drain the old fuel from the tank completely.
- Use a siphon pump or carefully tip the mower to pour it into an approved container.
- Add fresh, clean gasoline with an octane rating recommended by your manufacturer. For most mowers, regular 87-octane is fine.
- Consider using a fuel stabilizer if you plan to store the mower for more than a month.
Problem 2: A Clogged Or Dirty Carburetor
When stale fuel evaporates, it leaves behind sticky residues. These residues clog the carburetor jets and float bowl, preventing the proper mix of air and fuel from reaching the engine. You’ll often here a sputtering sound if this is the issue.
- Remove the air filter cover and the filter itself to access the carburetor.
- Locate the carburetor bowl (usually a small, bulb-shaped metal cup underneath).
- Place a container underneath and remove the bowl nut to drain any old fuel.
- Clean the bowl and the small jet inside with carburetor cleaner and a soft wire.
- Reassemble and try starting the mower. For severe clogs, the entire carburetor may need a soak or replacement.
Problem 3: Faulty Or Dirty Spark Plug
The spark plug provides the ignition source for the fuel in the cylinder. A dirty, fouled, or damaged plug won’t create a strong enough spark. This is a very easy and inexpensive part to check and replace.
First, disconnect the spark plug wire. Then, use a spark plug socket to remove the plug. Inspect it. The electrode should not be covered in black soot or have a cracked porcelain insulator. If it looks dirty, you can clean it with a wire brush. Check the gap with a feeler gauge and adjust it to your mower’s specification (often .030 inches). If in doubt, simply replace it with a new plug of the correct type. A fresh spark plug can make a world of difference.
Problem 4: Dirty Air Filter
A clogged air filter starves the engine of oxygen. The fuel-air mixture becomes too “rich” (too much fuel, not enough air) to ignite properly. This is another simple fix. Remove the air filter cover and take out the filter. If it’s a paper filter, hold it up to the light. If you can’t see light through it, it needs to be replaced. If it’s a foam filter, you can wash it in warm, soapy water, rinse it thoroughly, let it dry completely, and then apply a few drops of clean engine oil before reinstalling. Never run the engine without the air filter.
Problem 5: Ignition Coil Failure
The ignition coil (or magneto) is what generates the electrical current for the spark plug. If it fails, no spark is produced. You can test for spark by carefully removing the spark plug, reconnecting it to the wire, and resting the metal body of the plug against the engine block. Pull the starter cord and look for a bright blue spark jumping the gap. If you see no spark, and you’ve already replaced the plug, the ignition coil is likely the culprit. Replacing an ignition coil is more advanced and may require specific tools.
Problem 6: Engine Flooding
Sometimes, you can have too much of a good thing. If you’ve pulled the starter cord repeatedly with the choke on, you may have flooded the engine with excess fuel. The smell of gasoline is a strong indicator. To fix this, move the throttle or choke lever to the “Fast” or “Open” position. Then, pull the starter cord slowly several times without engaging the engine to help clear the cylinder. Wait 15-20 minutes for the fuel to evaporate, then try starting normally without using the choke.
Problem 7: A Weak Or Dead Battery (For Electric Start Mowers)
If your mower has an electric start button and you hear only a clicking sound or nothing at all, the battery is the first suspect. Check the battery terminals for corrosion (a white or bluish powdery substance) and clean them with a wire brush. Use a multimeter to test the battery voltage. A 12-volt battery should read at least 12.6 volts when fully charged. If it’s low, recharge it with a compatible battery charger. If the battery is old (over 3 years), it may not hold a charge and will need replacement.
Problem 8: Faulty Recoil Starter Assembly
The recoil starter is the assembly with the pull cord. If the cord is broken, the pulley inside is jammed, or the recoil spring is broken, the engine won’t turn over. You might feel no resistance when you pull, or the cord may not retract. Repairing a recoil starter involves disassembling the housing and requires careful handling of the tensioned spring. For many, replacing the entire starter assembly is the safer, easier option.
Additional Mechanical Issues
If you’ve checked all the common issues above and your mower still won’t start, the problem could be more serious. Internal engine problems like a sheared flywheel key (which throws off ignition timing), a stuck valve, or loss of compression require significant mechanical skill and tools to diagnose and repair. At this point, consulting a professional small engine repair shop is often the most practical solution.
Preventative Maintenance To Avoid Future Problems
The best way to avoid the “no-start” headache is with proper end-of-season care. A little preparation in the fall ensures an easy start in the spring.
- Add a fuel stabilizer to a full tank of gas and run the engine for 5 minutes to circulate it through the carburetor.
- Disconnect the spark plug wire and remove the spark plug. Add a tablespoon of engine oil into the cylinder, then slowly pull the starter cord a few times to coat the cylinder walls. Reinstall the plug (but not the wire).
- Change the engine oil while it’s warm at the end of the season, not the begining.
- Clean the mower deck thoroughly to remove grass clippings, which hold moisture and cause rust.
- Store the mower in a dry, covered place.
Frequently Asked Questions
Why won’t my lawn mower start after winter?
This is almost always due to stale gasoline clogging the carburetor. The fuel breaks down during storage. Draining the old gas or using a stabilizer before storage prevents this.
Why does my lawn mower start but then die?
This typically points to a fuel delivery issue. The engine uses the fuel in the carburetor bowl to start, but then can’t draw more from the tank. Causes include a clogged fuel filter, a stuck carburetor float, or a blocked fuel tank vent.
Why won’t my lawn mower start even with starting fluid?
If the mower briefly starts with starting fluid but then dies, it confirms a fuel system problem (clogged carburetor, bad fuel). If it doesn’t react at all to starting fluid, you likely have an ignition problem, like a bad spark plug or ignition coil.
What should I check first when my mower won’t start?
Always follow a SAFE order: 1) Check for fresh gas. 2) Check the spark plug. 3) Check the air filter. 4) Check the carburetor. Also, ensure all safety levers are engaged correctly and the battery (if electric start) is charged.
How do I know if my lawn mower carburetor is bad?
Signs include the engine not starting, starting then stalling, running rough, or leaking fuel. Often, a thorough cleaning solves the problem. If cleaning doesn’t work, or the carburetor body is damaged, replacement is necessary.