Is your lawn mower refusing to cooperate, leaving your lawn looking less than perfect? You’re not alone! A lawn mower that won’t start is a common frustration for homeowners, and in fact, according to a recent survey by the Outdoor Power Equipment Institute (OPEI), starting problems are among the top three reasons why lawn mowers need repair. A well-maintained lawn is the pride of many homeowners, and a faulty lawn mower can quickly turn that pride into a headache. Getting your mower running again doesn’t have to be a mystery, however. In this comprehensive guide, we’ll explore six of the most frequent reasons why your lawn mower might be failing to start, providing you with clear symptoms, diagnostic methods, must-have mower parts, and step-by-step solutions. Whether you have a push mower or a riding mower, understanding these common issues can save you time and money on repairs, so let’s dive in!
Also read: 10 Essential Spring Lawn Mower Parts You Must Have
Why Is My Lawn Mower Smoking? Diagnose & Fix
*Scroll to the bottom of the article to see the lawn mower won’t start full summary table.
1. Fuel Problems: Old Fuel & Clogged Fuel Filter
The engine cranks but doesn’t start, sputters and dies shortly after starting, or runs unevenly, indicating a potential fuel issue. Your lawn mower relies on a steady supply of clean fuel to function correctly, and therefore, several fuel-related issues can prevent it from starting. One of the most common reasons is simply old fuel, as gasoline can degrade over time, especially when left sitting in the tank for extended periods. This is because the volatile components evaporate, leaving behind a gummy residue that can clog the carburetor and fuel lines. Furthermore, a blocked fuel cap vent can create a vacuum in the tank, preventing fuel from flowing to the carburetor, and a dirty fuel filter restricts fuel flow, starving the engine of the fuel it needs to run.
Diagnosis:
You should check the fuel level, because this might seem obvious, but ensure you have enough gas in the tank! Next, you should assess fuel quality, as old or stale fuel is a common culprit, especially after winter storage. Then, inspect the fuel cap, because a clogged fuel cap vent can create a vacuum in the tank, preventing fuel from flowing to the carburetor. After that, examine the fuel filter, as a dirty or clogged fuel filter restricts fuel flow, starving the engine of fuel. Finally, perform a carburetor check, because the carburetor mixes fuel and air for combustion, and it’s a complex component, so stale fuel can leave residue that clogs its tiny passages.
How to clean a carburetor? Please read: How to Clean a Honda Lawn Mower Carburetor? A Step-by-Step Guide
Solutions:
First, drain the old fuel, because if the fuel is old or suspect, you should drain the tank completely and dispose of it properly. Then, refill with fresh fuel, using fresh gasoline with a fuel stabilizer like STA-BIL to keep it fresh for longer. According to STA-BIL, their fuel stabilizer can keep fuel fresh for up to 24 months, preventing gum and varnish buildup. Next, clean or replace the fuel cap, trying to loosen the fuel cap to see if the engine starts, and if so, clean or replace the cap. After that, replace the fuel filter, because a new fuel filter is an inexpensive way to ensure clean fuel delivery. Finally, clean the carburetor, as this can be a DIY task with carburetor cleaner, but if you’re not comfortable, take it to a professional. For instance, many older Briggs & Stratton engines are particularly susceptible to carburetor clogs due to their design.
2. Worn-Out Spark Plug
If the engine of your lawn mower won’t start at all, it is a clear indication of a potential spark plug problem. The spark plug provides the spark that ignites the fuel-air mixture in the engine, and therefore, a faulty spark plug will prevent combustion. Spark plugs can fail for a variety of reasons, including carbon fouling, oil contamination, or simply old age. Moreover, a cracked or damaged spark plug insulator can also prevent the spark from reaching the combustion chamber.
Diagnosis:
First, inspect the spark plug, removing the spark plug and checking for cracks, dirt, carbon buildup, or corrosion. A wet plug indicates a fuel system issue, while a dry plug suggests a fuel delivery problem. Then, test for spark, using a spark tester to check if the spark plug is producing a strong, consistent spark.
Solutions:
If the plug is dirty, you can clean it with a wire brush and some rubbing alcohol. Then, replace the spark plug, because if the plug is damaged, corroded, or doesn’t produce a spark, you should replace it with a new one, ensuring the new plug is the correct type for your mower. Finally, check the spark plug gap, using a spark plug gap tool to ensure the gap between the electrodes is set to the manufacturer’s specification. A properly gapped spark plug ensures optimal combustion.
3. Air Filter Problems
Is your engine cranks but doesn’t start, loses power during operation, runs roughly, or emits black smoke? All of which point to a potential air filter issue. The air filter prevents dirt and debris from entering the engine, and consequently, a clogged air filter restricts airflow, disrupting the air-fuel mixture and causing starting problems. When the air filter is clogged, the engine is starved of oxygen, leading to incomplete combustion and reduced power.
Diagnosis:
Inspect the air filter, removing the air filter and checking for dirt, dust, grass clippings, and other debris.
Solutions:
If the filter is only lightly soiled, you can clean it by tapping it gently or using compressed air; however, if the filter is heavily soiled or damaged, you should replace it with a new one. For example, foam air filters can be washed with soap and water, while paper filters should be replaced.
Also read: How to Clean and Replace the Air Filter For John Deere Mower (Complete Guide)
4. Battery/Starting System Issues (Riding Mowers):
Lawn mower won’t start? The battery is to blame! What are the symptoms of battery issues? The engine won’t crank, you hear a clicking sound when trying to start, or the engine cranks very slowly, indicating a problem with the battery or starting system. Riding mowers rely on a battery and starter motor to crank the engine, and therefore, problems with the battery, connections, or starter system can prevent the mower from starting. Batteries can lose their charge over time, especially if they are not properly maintained or if the mower is stored for long periods without being used. Additionally, corroded battery terminals can prevent the flow of electricity, and a faulty starter motor can fail to crank the engine.
Diagnosis:
First, check battery connections, ensuring the battery cables are securely connected to the battery terminals and free of corrosion. Then, test battery voltage, using a multimeter to check the battery voltage, because a fully charged 12-volt battery should read around 12.6 volts. Finally, check safety interlocks, because riding mowers have safety switches that prevent the engine from starting unless certain conditions are met (e.g., blade disengaged, parking brake engaged, operator in the seat).
Solutions:
Cleaning battery terminals is what comes first. Clean any corrosion from the battery terminals with a wire brush and a solution of baking soda and water. Then, charge the battery using a battery charger to charge the battery fully. Next, replace the battery, because if the battery is old or won’t hold a charge, you should replace it with a new one. After that, check and repair wiring, inspecting the wiring for any damage or loose connections. Finally, check the solenoid, because the solenoid sends power to the starter motor, and if it’s faulty, the mower won’t start.
You might be interested: How to Sharpen Lawn Mower Blades Correctly (Beginner)
5. Blocked Mower Deck or Blades
If you find the starter rope is very hard to pull, the engine stalls immediately after starting, or the mower cuts unevenly, all of which suggest a blocked mower deck or blades. When it happens, an accumulation of grass clippings and debris under the mower deck can obstruct the blades, making it difficult for the engine to turn over, and in some cases, the buildup can be so severe that it completely prevents the blades from rotating.
Diagnosis:
First, inspect under the deck, carefully inspecting the underside of the mower deck for excessive grass buildup. Then, check the blades, ensuring the blades are free to rotate and not obstructed by tangled grass or other debris.
Solutions:
First, clean the mower deck, using a scraper or pressure washer to remove accumulated grass and debris from the underside of the mower deck. Then, remove obstructions from blades, clearing any tangled grass or debris from around the blades.
6. Broken Flywheel Key: Protecting the Engine
The flywheel key is a small metal piece that connects the crankshaft to the flywheel. How to tell if it is bad? The engine suddenly stops running, especially after hitting a hard object. The engine might turn over, but it won’t start. The flywheel key’s primary function is to ensure that the flywheel and crankshaft rotate in sync. However, if your mower hits a hard object, such as a rock or a tree root, the sudden impact can put excessive stress on the engine. To prevent more serious engine damage, the flywheel key is designed to shear or break, acting as a sacrificial component. This prevents the crankshaft and flywheel from rotating out of sync, which could cause significant internal damage. Therefore, if the flywheel key is broken, the engine will not be able to start, as the timing will be off.
Diagnosis:
To diagnose a broken flywheel key, first, remove the spark plug wire to prevent accidental starting. Then, remove the flywheel cover and inspect the flywheel key. If the key is sheared or broken, it will be visibly damaged. You may need a flywheel puller to remove the flywheel for a better inspection.
Solutions:
First, replace the broken flywheel key with a new one. Ensure that you use the correct flywheel key for your specific lawn mower model. Then, reassemble the flywheel and flywheel cover, and reconnect the spark plug wire.
7. Other Potential Issues: The Little Things
Several other factors can contribute to a lawn mower that won’t start. For example, a low oil level can trigger a safety switch that prevents the engine from starting, and a faulty start switch could also prevent the mower from starting. Furthermore, low engine compression can prevent starting, though this usually requires professional diagnosis, and an obstruction in the exhaust pipe or muffler can also cause starting problems.
Lawn Mower Maintenance Seasonal Advice
- Starting After Winter Storage: After winter, thoroughly inspect the mower, change the oil, replace the spark plug, and use fresh fuel with a stabilizer. For example, many people find that spraying a little starting fluid into the carburetor can help get the engine running after a long period of inactivity.
- Mowing in Hot Weather: Avoid mowing during the hottest part of the day to prevent overheating. Ensure the air filter is clean to promote proper airflow.
Troubleshooting Comparison Table
| Problem | Symptoms | Diagnosis | Solution |
|---|---|---|---|
| Fuel Issues | Cranks but doesn’t start, sputters, runs unevenly | Check fuel level, quality, cap, filter, carburetor | Drain old fuel, replace with fresh, clean/replace cap/filter/carburetor |
| Spark Plug Issues | Won’t start at all | Inspect spark plug, test for spark | Clean/replace spark plug, check gap |
| Air Filter Issues | Cranks but doesn’t start, loses power, runs roughly | Inspect air filter | Clean/replace air filter |
| Battery (Riding Mowers) | Won’t crank, clicking sound, slow cranking | Check connections, voltage, safety interlocks | Clean terminals, charge/replace battery, check wiring |
| Blocked Mower Deck | Hard to pull rope, stalls, uneven cutting | Inspect under deck, check blades | Clean deck, remove obstructions |
| Broken Flywheel Key | Engine suddenly stops, especially after hitting something hard | Remove flywheel cover and inspect the flywheel key for damage | Replace the broken flywheel key |
| Other Issues | Varies | Check oil level, start switch, compression, exhaust | Address specific issue |
Preventative Maintenance Tips
To keep your lawn mower running smoothly, use fuel stabilizer, adding it to your gas can to keep your fuel fresh, especially during the off-season. Also, regularly clean or replace the air filter, as a clean air filter ensures optimal engine performance. Furthermore, change the oil regularly, following the manufacturer’s recommendations for oil changes, and sharpen blades, because sharp blades make for a cleaner cut and reduce strain on the engine. Finally, winterize your mower, because before storing your mower for the winter, you should drain the fuel, change the oil, and clean the mower deck.
Conclusion
We at FridayParts understand how frustrating it can be when your lawn mower won’t start, and that’s why we’re committed to providing you with high-quality lawn mower parts at competitive prices. Whether you need a new spark plug, air filter, carburetor, or any other replacement part, we have you covered. We’ve seen countless customers get their mowers back in action with our parts, and we’re confident we can help you too. Browse our wide selection of lawn mower parts today and get your mower running like new!
More lawn mower posts: Is It Worth Buying a Robotic Lawnmower?
