Few things are more frustrating than a lawn mower that cranks enthusiastically but refuses to roar to life. You pull the cord, the engine spins, but nothing. You check the fuel, everything seems fine, yet still, no luck. This common problem can be maddening, but understanding the possible causes and knowing how to troubleshoot them can save you time, money, and a whole lot of frustration. So, let’s dive into the potential culprits and get your mower back in action.
Understanding the Basics: What “Turns Over” Really Means
Before we start diagnosing, let’s clarify what “turns over” means. When you hear the engine cranking or turning, it signifies that the starter motor is functioning and successfully rotating the engine’s crankshaft. This is a crucial piece of information because it eliminates several potential problems, primarily those related to the battery (if you have an electric start mower) or the starter motor itself. If the engine isn’t turning over at all, that points to a completely different set of issues.
The fact that your mower is turning over means the starter system is doing its job. This narrows down the possibilities considerably, allowing us to focus on the components critical for combustion: fuel, air, and spark.
The Fuel System: The Lifeblood of Your Mower
The most common reason for a mower that turns over but won’t start is a problem within the fuel system. Gasoline, especially when left sitting for extended periods, can degrade and become gummy, clogging vital components.
Checking the Fuel Itself
The first step is to examine the fuel itself. Smell the gasoline in the tank. Does it smell fresh, or does it have a stale, varnish-like odor? If it smells bad, drain the old fuel and replace it with fresh gasoline. Always use the correct octane rating recommended by your mower’s manufacturer. Old fuel is a very common culprit, especially after winter storage. It can wreak havoc on the small passageways within the carburetor.
Fuel Lines and Fuel Filter
Once you’ve addressed the fuel quality, inspect the fuel lines. Look for cracks, kinks, or any signs of damage. A compromised fuel line can prevent fuel from reaching the carburetor. If you find any problems, replace the fuel line. Many mowers also have a small fuel filter, often located inline between the fuel tank and the carburetor. A clogged fuel filter can severely restrict fuel flow. Remove the filter and check for debris. If it’s dirty, replace it. Fuel filters are inexpensive and should be replaced annually as part of regular maintenance.
The Carburetor: The Heart of the Fuel System
The carburetor’s job is to mix fuel and air in the correct ratio for combustion. This is a precision process, and even a small amount of dirt or debris can disrupt it. Carburetors are notoriously sensitive to old fuel. The tiny jets and passageways can easily become clogged, preventing the engine from getting the fuel it needs.
If you suspect a carburetor issue, try cleaning it. Many carburetors can be carefully disassembled for cleaning. Use carburetor cleaner spray and small brushes or wires to clear any blockages. Pay particular attention to the jets. If you’re not comfortable disassembling the carburetor, you can try spraying carburetor cleaner into the air intake while cranking the engine. Sometimes, this will dislodge enough debris to get the mower started. However, a thorough cleaning or even carburetor replacement might be necessary if the problem persists.
Fuel Pump Considerations
Some mowers have a fuel pump to help move fuel from the tank to the carburetor. These pumps are often vacuum-operated, using the engine’s vacuum to draw fuel. If the fuel pump is faulty, it won’t be able to deliver fuel effectively. To test the fuel pump, disconnect the fuel line from the carburetor and crank the engine. You should see fuel pulsing out of the fuel line. If not, the fuel pump might be the problem.
The Ignition System: Sparking the Combustion
Even with the right fuel and air mixture, you need a spark to ignite it. Problems with the ignition system are another common reason for a mower that turns over but won’t start.
Checking the Spark Plug
The spark plug is the component that delivers the electrical spark to the combustion chamber. A fouled, damaged, or improperly gapped spark plug can prevent the engine from starting. Remove the spark plug and inspect it. Look for signs of carbon buildup, oil fouling, or cracks in the ceramic insulator. If the spark plug is dirty, clean it with a wire brush or replace it. Check the spark plug gap using a feeler gauge and adjust it to the manufacturer’s specifications.
To test if the spark plug is working, connect the spark plug wire to the spark plug, ground the spark plug against the engine block, and crank the engine. You should see a strong, blue spark. If you don’t see a spark, or if the spark is weak and yellow, the spark plug is likely faulty and needs to be replaced. A weak spark can also indicate problems with the ignition coil.
Ignition Coil Issues
The ignition coil is responsible for generating the high voltage needed to create a spark at the spark plug. If the ignition coil is failing, it might not produce enough voltage to create a spark, even if the spark plug is good. Testing the ignition coil usually requires specialized tools and knowledge. However, a common test is to check the resistance of the coil using a multimeter. Consult your mower’s service manual for the correct resistance values. If the resistance is outside the specified range, the ignition coil needs to be replaced.
Kill Switch and Safety Interlocks
Modern lawn mowers are equipped with kill switches and safety interlocks to prevent accidental starts. These switches are designed to stop the engine if certain conditions aren’t met, such as the operator not being present, the bail handle not being engaged, or the mower being in gear. Check all the safety switches to ensure they are functioning correctly. A faulty kill switch or safety interlock can prevent the engine from starting, even if everything else is working properly.
The Air Intake: Ensuring Proper Airflow
While less common, a problem with the air intake can also prevent a mower from starting. The engine needs a sufficient supply of air to mix with the fuel for combustion.
Air Filter Inspection
The air filter prevents dirt and debris from entering the engine. A clogged air filter can restrict airflow, leading to a rich fuel mixture (too much fuel, not enough air) that can make the engine difficult to start. Remove the air filter and inspect it. If it’s dirty, clean it or replace it. Foam air filters can usually be cleaned with soap and water, while paper air filters should be replaced.
Checking for Obstructions
Ensure that there are no obstructions in the air intake pathway. Check for debris, such as leaves or grass clippings, that might be blocking the airflow.
Other Potential Causes
While fuel, spark, and air are the primary suspects, other factors can also contribute to a mower that turns over but won’t start.
Low Compression
Compression is the measure of how tightly the air/fuel mixture is squeezed within the cylinder before ignition. Low compression makes it difficult for the engine to ignite the fuel mixture. This is usually due to worn piston rings or damaged valves. Checking compression requires a compression tester and is a more advanced diagnostic procedure. If you suspect low compression, it’s best to consult a qualified mechanic.
Sheared Flywheel Key
The flywheel key is a small key that connects the flywheel to the crankshaft. If this key shears, it can throw off the engine timing and prevent it from starting. This is less common, but it’s a possibility, especially if the mower has recently hit a hard object.
A Systematic Approach to Troubleshooting
When faced with a mower that turns over but won’t start, it’s best to follow a systematic approach to troubleshooting.
- Start with the obvious: Check the fuel level and make sure the fuel valve is open. Ensure the spark plug wire is securely connected.
- Address the fuel system: Check the fuel quality, fuel lines, and fuel filter. Clean or replace the carburetor if necessary.
- Inspect the ignition system: Check the spark plug for fouling, damage, and proper gap. Test the spark plug for spark. Investigate the ignition coil if necessary.
- Examine the air intake: Check the air filter for cleanliness and ensure there are no obstructions in the air intake.
- Consider other potential causes: If the above steps don’t resolve the problem, consider low compression or a sheared flywheel key.
Prevention is Key: Regular Maintenance
The best way to avoid a mower that turns over but won’t start is to perform regular maintenance.
- Use fresh fuel: Always use fresh fuel, and add a fuel stabilizer if you’re storing the mower for an extended period.
- Change the air filter regularly: A clean air filter ensures proper airflow and prevents dirt from entering the engine.
- Replace the spark plug annually: A new spark plug ensures a strong spark and efficient combustion.
- Clean the carburetor: Regularly clean the carburetor to prevent clogs and ensure proper fuel delivery.
- Sharpen the blade: A sharp blade reduces the strain on the engine and improves cutting performance.
- Change the oil: Regularly changing the oil lubricates the engine and prevents wear.
By following these maintenance tips, you can keep your lawn mower running smoothly for years to come and avoid the frustration of a mower that turns over but won’t start. Remember safety first, disconnect the spark plug before working on the mower and consult your owner’s manual for specific instructions for your model. Good luck, and happy mowing!
Why won’t my lawn mower start after it tipped over?
The most common reason a lawn mower won’t start after being tipped over is oil flooding the engine cylinder and carburetor. When a lawn mower is tilted excessively, oil can seep into areas where it shouldn’t be, like the combustion chamber. This excess oil fouls the spark plug, preventing it from generating a spark, and also makes it difficult for the engine to compress the air-fuel mixture properly.
To resolve this, start by removing the spark plug and carefully cleaning it with a wire brush or spark plug cleaner. Pull the starter cord several times to expel any excess oil from the cylinder. Let the mower sit for a while (30 minutes to an hour) to allow the oil to drain back into the crankcase. Once you’ve completed these steps, replace the spark plug and try starting the mower again.
How do I prevent this problem from happening again?
The best way to prevent oil from flooding the engine is to avoid tipping the mower excessively in the first place. When working on the underside of the mower, try to tilt it so that the carburetor and air filter are facing upwards. This prevents oil from flowing into these sensitive components.
Alternatively, consider using a lawn mower lift. These lifts allow you to safely raise the mower, providing easy access to the blade without tilting it over. Following these practices significantly reduces the risk of flooding the engine with oil and needing to troubleshoot starting problems later.
What if cleaning the spark plug doesn’t work?
If cleaning the spark plug doesn’t solve the problem, the spark plug itself might be damaged or fouled beyond repair. Tipping the mower can cause the spark plug to become excessively oily, making it difficult to clean effectively. A damaged spark plug won’t produce the necessary spark to ignite the fuel.
In this case, replacing the spark plug is the next logical step. Ensure you purchase the correct spark plug for your specific lawn mower model. Installing a new spark plug eliminates the possibility of a faulty spark plug being the cause of the problem, allowing you to proceed with other troubleshooting steps if necessary.
Could fuel be the problem even though the mower tipped?
Yes, while oil flooding is the most common culprit, fuel-related issues can also arise when a lawn mower tips over. Tilting the mower can disrupt the fuel system, potentially causing fuel to leak into the carburetor or flood the engine with too much fuel. Furthermore, old or contaminated fuel can exacerbate starting problems.
Check the fuel filter and fuel lines for any obstructions or damage. If the fuel is old or looks discolored, drain the fuel tank and replace it with fresh fuel. Old fuel can lose its volatility and become difficult to ignite, especially after the mower has been tipped. Replacing the fuel is a simple step that can often resolve starting issues.
Is there a safety feature that might be preventing the mower from starting?
Many modern lawn mowers are equipped with safety features designed to prevent accidental starts. One common feature is the blade brake clutch (BBC), which disengages the blade and stops the engine if the operator releases the handle. If the cable or mechanism for the BBC is damaged or malfunctioning, it can prevent the mower from starting, even after being uprighted.
Check the operator presence control (OPC) lever and cable to ensure they are functioning correctly. Make sure the lever is fully engaged when starting the mower. If the cable is loose, damaged, or disconnected, it may need to be adjusted or replaced. Also, some mowers have an oil sensor that prevents starting if the oil level is too low. Even if you changed the oil recently, check the oil level to be sure.
What if I still can’t start the mower after trying these steps?
If you’ve cleaned or replaced the spark plug, checked the fuel and safety features, and the lawn mower still won’t start, it might indicate a more serious problem. The carburetor could be clogged or damaged, requiring professional cleaning or replacement. There could also be internal engine damage caused by the oil flooding, although this is less common.
At this point, it’s best to consult a qualified lawn mower repair technician. They have the expertise and tools to diagnose and repair more complex issues. Attempting to fix internal engine problems yourself without the proper knowledge and equipment could potentially cause further damage.
Could the air filter be the reason it won’t start?
Yes, although less common than oil flooding, a dirty or oil-soaked air filter can prevent a lawn mower from starting after being tipped over. When the mower is tilted, oil can sometimes saturate the air filter, restricting airflow to the engine. A clogged or restricted air filter reduces the amount of air reaching the combustion chamber, disrupting the air-fuel mixture needed for ignition.
Inspect the air filter for signs of oil saturation or excessive dirt. If it’s dirty, clean it thoroughly or replace it with a new one. If it’s soaked in oil, it’s best to replace it, as cleaning might not fully restore its functionality. A clean air filter ensures proper airflow, helping the engine start and run smoothly.