A lawnmower that cranks but refuses to start can be incredibly frustrating, especially when you’re eager to tackle your yard work. That tell-tale “whirr-whirr-whirr” followed by nothing but silence is a common issue, and thankfully, often resolvable with a little troubleshooting. This guide will walk you through the most likely culprits and offer practical solutions to get your mower roaring back to life.
Fuel System Problems: Starvation at the Heart of the Issue
One of the most frequent reasons a mower turns over but won’t start lies within the fuel system. The engine needs a consistent supply of fuel to ignite, and any interruption can cause a no-start condition.
Old or Stale Fuel: The Silent Saboteur
Gasoline degrades over time, especially when exposed to air. This process leads to the formation of varnish and gum deposits that can clog fuel lines, carburetors, and other critical components. Always use fresh gasoline, ideally stabilized with a fuel stabilizer if it’s going to sit for an extended period. If your mower has been sitting idle for several months, this is the first place to investigate.
How to check and fix:
Smell the fuel. Does it smell “off” or stale? If so, drain the old fuel from the tank completely. Add fresh fuel and try starting the mower. If it still doesn’t start, you might need to clean the carburetor. Consider adding a fuel stabilizer to the new gasoline to prevent future degradation.
Clogged Fuel Filter: A Small Part, a Big Problem
The fuel filter is designed to prevent debris from entering the carburetor. Over time, this filter can become clogged with dirt, rust, and other contaminants, restricting fuel flow. A blocked fuel filter can starve the engine, preventing it from starting.
How to check and fix:
Locate the fuel filter, typically in-line between the fuel tank and the carburetor. Disconnect the fuel lines from the filter (be prepared for some fuel spillage). Inspect the filter. If it appears dirty or clogged, replace it with a new one. Make sure to install the new filter in the correct direction, following the arrow on the filter body.
Carburetor Issues: The Fuel-Air Mixing Maestro
The carburetor is responsible for mixing fuel and air in the correct ratio for combustion. A dirty or clogged carburetor is a common cause of starting problems, particularly in mowers that have been stored for a long time. Varnish and gum deposits from old fuel can restrict fuel flow through the tiny passages within the carburetor.
How to check and fix:
First, try using carburetor cleaner. Spray carburetor cleaner into the carburetor intake while attempting to start the mower. If it starts briefly and then dies, it’s a good indication that the carburetor is clogged.
For a more thorough cleaning, you may need to remove the carburetor and disassemble it. This requires some mechanical aptitude and care. Clean all parts thoroughly with carburetor cleaner and compressed air. Pay close attention to the jets and passages. Reassemble the carburetor and reinstall it on the mower.
If you’re not comfortable disassembling the carburetor, you can take it to a professional for cleaning or replacement.
Fuel Line Problems: The Highway for Fuel
Cracked, kinked, or disconnected fuel lines can also prevent fuel from reaching the engine. Inspect the fuel lines from the tank to the carburetor for any signs of damage or leaks.
How to check and fix:
Visually inspect the fuel lines for cracks, kinks, or loose connections. Replace any damaged fuel lines. Ensure that all fuel lines are securely connected to the fuel tank, fuel filter, and carburetor.
Ignition System Woes: Sparking the Flame of Life
Even with a proper fuel supply, the engine needs a spark to ignite the fuel-air mixture. Problems with the ignition system can prevent the mower from starting.
Spark Plug Issues: The Initiator of Combustion
The spark plug provides the spark that ignites the fuel-air mixture in the cylinder. A fouled, worn, or improperly gapped spark plug can prevent the engine from starting.
How to check and fix:
Remove the spark plug. Inspect it for signs of fouling (carbon buildup, oil, or fuel). Clean the spark plug with a wire brush or replace it with a new one. Check the spark plug gap with a spark plug gap tool. Adjust the gap to the manufacturer’s specifications.
To test if the spark plug is firing, connect the spark plug wire to the spark plug. Hold the spark plug against the engine block (make sure it’s making good contact with metal). Pull the starter cord. You should see a bright blue spark jump across the spark plug gap. If there is no spark or a weak spark, the spark plug is faulty and needs to be replaced, or there could be an issue with the ignition coil.
Ignition Coil Failure: The Spark Plug’s Power Source
The ignition coil generates the high voltage needed to create a spark at the spark plug. A faulty ignition coil can prevent the engine from starting.
How to check and fix:
Testing an ignition coil requires a multimeter. Disconnect the spark plug wire from the spark plug. Set the multimeter to measure resistance (ohms). Check the primary and secondary resistance of the ignition coil according to the manufacturer’s specifications. If the resistance readings are outside the specified range, the ignition coil is likely faulty and needs to be replaced.
If you’re not comfortable testing the ignition coil yourself, take the mower to a professional.
Safety Switches: Preventing Accidental Starts
Most mowers have safety switches that prevent the engine from starting if certain conditions are not met, such as the blade being engaged or the operator not being present. A faulty safety switch can prevent the mower from starting even if everything else is working properly.
How to check and fix:
Locate the safety switches on your mower (typically located on the handle, seat, or blade engagement lever). Inspect the switches for damage or loose connections. Test the switches with a multimeter to ensure they are functioning properly. If a switch is faulty, replace it.
Other Potential Culprits: Digging Deeper
If you’ve ruled out fuel and ignition problems, there are a few other potential causes to consider.
Low Oil Level: Protecting the Engine’s Lifeblood
Many mowers have a low-oil sensor that prevents the engine from starting if the oil level is too low. This is to protect the engine from damage due to insufficient lubrication.
How to check and fix:
Check the oil level using the dipstick. If the oil level is low, add oil to the correct level. Make sure to use the correct type of oil as specified in the owner’s manual.
Blocked Air Filter: Suffocating the Engine
A dirty or clogged air filter can restrict airflow to the engine, preventing it from starting. A blocked air filter starves the engine of oxygen, hindering combustion.
How to check and fix:
Remove the air filter. Inspect it for dirt and debris. Clean the air filter by tapping it gently or blowing it out with compressed air. If the air filter is heavily soiled or damaged, replace it.
Compression Issues: The Engine’s Ability to Squeeze
While less common, a loss of compression can also prevent the mower from starting. This could be due to worn piston rings, a damaged cylinder, or a faulty valve.
How to check and fix:
Checking compression requires a compression tester. Remove the spark plug. Insert the compression tester into the spark plug hole. Pull the starter cord several times to build up pressure. Read the compression reading on the gauge. Compare the reading to the manufacturer’s specifications. If the compression is low, it indicates a problem with the engine’s internal components.
Compression issues are typically more serious and may require professional repair.
Choke Problems: Starting in Cold Conditions
The choke helps to enrich the fuel mixture when starting a cold engine. A faulty choke mechanism can prevent the engine from starting, especially in cold weather.
How to check and fix:
Ensure the choke is properly engaging when starting a cold engine. If the choke is manually operated, make sure you are using it correctly. If the choke is automatic, check the linkage and ensure it is moving freely. A choke that is stuck open or closed can cause starting problems.
Preventative Maintenance: Keeping Your Mower Running Smoothly
The best way to avoid starting problems is to perform regular preventative maintenance on your mower.
Regular maintenance includes:
- Changing the oil regularly (every 25-50 hours of use)
- Replacing the air filter as needed
- Replacing the spark plug annually
- Using fresh fuel and adding fuel stabilizer when storing the mower
- Cleaning the mower deck and undercarriage after each use
By following these simple steps, you can keep your mower running smoothly for years to come and avoid the frustration of a mower that turns over but won’t start.
Troubleshooting a mower that cranks but doesn’t start can be daunting, but with a methodical approach, you can often identify and fix the problem yourself. Remember to always prioritize safety when working on your mower. Disconnect the spark plug wire before performing any repairs and wear appropriate safety gear. If you’re not comfortable performing any of these repairs yourself, take your mower to a qualified technician.
Why won’t my lawnmower start, even though it’s turning over?
The most common reason for a lawnmower to turn over but not start is a lack of proper fuel or spark. This could be due to stale fuel that has lost its combustibility, a clogged carburetor preventing fuel from reaching the engine, a faulty spark plug that isn’t generating a spark, or a problem with the ignition system preventing the spark plug from firing. Check the fuel first – if it smells old or has been sitting for a long time, drain it and replace it with fresh fuel.
Next, inspect the spark plug. Remove it and check for any signs of damage, fouling, or corrosion. Clean the spark plug if necessary, or replace it if it’s in poor condition. To test if the spark plug is working, reattach the spark plug wire and ground the spark plug against the engine while pulling the starter rope. You should see a spark jump across the gap if it’s functioning correctly.
How do I check if my lawnmower is getting fuel?
A simple way to check if fuel is reaching the engine is to prime the carburetor several times. If your mower has a primer bulb, push it a few times and then try starting the engine. If it starts briefly and then dies, it’s likely a fuel delivery issue. Alternatively, you can check the fuel lines for any kinks, cracks, or leaks.
Another method involves checking the carburetor bowl. Locate the carburetor bowl drain screw (usually at the bottom of the carburetor) and loosen it slightly. If fuel flows out, it indicates that fuel is at least reaching the carburetor. If no fuel comes out, there’s likely a blockage in the fuel line, fuel filter, or carburetor itself.
What could be causing a blockage in my lawnmower’s carburetor?
Carburetors are prone to clogs due to the small jets and passages within them. Over time, old fuel can break down and leave behind varnish or gum deposits that restrict fuel flow. This is especially common if the mower has been stored for an extended period without being properly prepared.
Another potential cause of blockage is debris entering the fuel system. This could be dirt, rust, or other contaminants that make their way into the fuel tank and eventually reach the carburetor. Using a fuel filter can help prevent debris from reaching the carburetor, but it’s still important to regularly clean or replace the filter.
How do I clean a lawnmower carburetor?
Before you start, disconnect the spark plug wire to prevent accidental starting. Then, carefully remove the carburetor from the engine. Take pictures as you disassemble it so you can easily reassemble it later. Use carburetor cleaner to thoroughly clean all the jets and passages.
Soak the carburetor components in carburetor cleaner for several hours or overnight, depending on the severity of the blockage. After soaking, use compressed air to blow out any remaining debris or cleaner. Reassemble the carburetor, making sure all parts are properly aligned and tightened.
What if my lawnmower has a clogged fuel filter?
A clogged fuel filter restricts the flow of fuel to the engine, causing starting problems or poor performance. The fuel filter is usually located in the fuel line between the fuel tank and the carburetor. It’s a small, inexpensive component that plays a crucial role in keeping the fuel system clean.
To check the fuel filter, remove it from the fuel line and inspect it for any signs of blockage. If the filter is visibly dirty or clogged, replace it with a new one. It’s generally recommended to replace the fuel filter annually as part of routine lawnmower maintenance.
How can I troubleshoot the ignition coil on my lawnmower?
The ignition coil is responsible for generating the high-voltage spark needed to ignite the fuel-air mixture in the engine. If the ignition coil is faulty, the spark plug won’t fire, and the engine won’t start. You can test the ignition coil using a multimeter to measure its resistance.
Consult your lawnmower’s service manual for the correct resistance values. If the measured resistance is outside the specified range, the ignition coil is likely faulty and needs to be replaced. You can also visually inspect the ignition coil for any signs of damage, such as cracks or melted plastic.
Why is the safety switch preventing my lawnmower from starting?
Lawnmowers are equipped with safety switches that prevent the engine from starting unless certain conditions are met. These switches are designed to protect the operator from accidental injuries. Common safety switches include the blade control lever switch, the operator presence control switch (on riding mowers), and the parking brake switch (on riding mowers).
If a safety switch is faulty or not properly engaged, it will prevent the engine from starting, even if the engine is turning over. Check all safety switches to ensure they are functioning correctly and properly engaged. For example, make sure the blade control lever is fully engaged and the operator is seated on the mower seat (if applicable).