A lawn mower that refuses to start is a frustrating experience, especially when the grass is growing rapidly. The seemingly simple task of pulling the cord should result in a roaring engine and neatly trimmed lawn. However, when that cord remains stubbornly unresponsive, or the engine sputters and dies, it’s time to investigate. This comprehensive guide delves into the most common reasons why your mower won’t start when you pull the cord, offering troubleshooting steps and solutions to get your machine back in action.
Fuel System Issues: The Prime Suspect
The fuel system is often the culprit behind starting problems. Like any internal combustion engine, your mower needs a reliable supply of fuel to run. Issues within this system can range from stale fuel to a clogged carburetor.
Stale Fuel: The Silent Saboteur
Gasoline degrades over time, especially when exposed to air. Stale fuel is a common cause of starting problems, particularly if your mower has been sitting idle for an extended period, such as over the winter. As fuel ages, it loses its volatility, making it harder to ignite. It can also form gummy deposits that clog fuel lines and carburetor jets.
The solution is simple: drain the old fuel and replace it with fresh gasoline. Consider adding a fuel stabilizer to prevent future degradation, especially if you anticipate storing the mower for more than a month. Fuel stabilizers work by preventing the oxidation of gasoline and keeping it fresh for longer. Be sure to check the manufacturer’s recommendations for the correct amount of stabilizer to use.
Clogged Fuel Lines: Fuel Delivery Blocked
Fuel lines are narrow tubes that transport fuel from the tank to the carburetor. These lines can become clogged with debris, such as dirt, rust, or gummy deposits from old fuel. A blockage in the fuel line will restrict the flow of fuel to the engine, preventing it from starting.
To check for a clogged fuel line, disconnect the fuel line from the carburetor and the fuel tank (ensure the fuel tank is nearly empty, or use a fuel shut-off valve if available). Inspect the line for any visible blockages or kinks. If you find debris, you can try blowing it out with compressed air or replacing the fuel line entirely. Fuel lines are relatively inexpensive and easy to replace.
The Carburetor: Where Air and Fuel Meet
The carburetor is a crucial component that mixes air and fuel in the correct ratio to create a combustible mixture. A clogged carburetor is a very common reason for starting problems. Small passages within the carburetor can become blocked by dirt, varnish, or gummy deposits from old fuel.
Cleaning a carburetor can be a delicate process. First, remove the air filter and inspect the carburetor visually. Look for any signs of dirt or buildup. You can try spraying carburetor cleaner into the carburetor throat while pulling the starter cord. If this doesn’t work, you may need to disassemble the carburetor and clean it thoroughly.
Carburetor cleaner is a solvent designed to dissolve varnish and deposits. Be sure to wear safety glasses and gloves when working with carburetor cleaner. If you are not comfortable disassembling the carburetor, you can take it to a small engine repair shop for professional cleaning. In some cases, replacing the carburetor may be the most cost-effective solution, especially for older mowers.
Fuel Filter: A Small Part, Big Impact
Many mowers have a fuel filter that sits in-line between the fuel tank and the carburetor. This filter traps dirt and debris, preventing them from entering the carburetor. A clogged fuel filter will restrict fuel flow and can prevent the mower from starting.
The fuel filter is a small, inexpensive part that is easy to replace. Locate the fuel filter on the fuel line and remove it. Inspect the filter for any signs of clogging. If it is dirty, replace it with a new fuel filter. It’s a good practice to replace the fuel filter annually as part of your regular mower maintenance.
Ignition System Issues: Sparking the Engine
The ignition system is responsible for creating the spark that ignites the air-fuel mixture in the cylinder. A faulty ignition system will prevent the engine from starting.
Spark Plug Problems: No Spark, No Start
The spark plug is a critical component of the ignition system. It delivers the electrical spark that ignites the air-fuel mixture. A fouled, damaged, or incorrectly gapped spark plug can prevent the mower from starting.
First, disconnect the spark plug wire. Then, use a spark plug wrench to remove the spark plug. Inspect the spark plug for any signs of damage, such as cracks or broken electrodes. Also, check for fouling, which is the buildup of carbon deposits on the spark plug. Clean the spark plug with a wire brush or replace it with a new one.
The spark plug gap is the distance between the center electrode and the ground electrode. An incorrect gap can prevent the spark plug from firing properly. Use a spark plug gap tool to ensure the gap is within the manufacturer’s specifications. The correct gap is usually specified in the owner’s manual or on a sticker on the mower.
To test if the spark plug is working, reconnect the spark plug wire and hold the spark plug against the engine block. Pull the starter cord and look for a spark at the spark plug electrode. If there is no spark, the spark plug is likely faulty and needs to be replaced. Remember to take precautions to avoid electric shock during this test.
Ignition Coil Failure: The Spark Generator
The ignition coil is responsible for generating the high-voltage electricity that is sent to the spark plug. A faulty ignition coil will prevent the spark plug from firing, resulting in a no-start condition.
Testing an ignition coil requires a multimeter. Disconnect the ignition coil from the spark plug wire and the engine wiring harness. Use the multimeter to measure the resistance of the ignition coil. Compare the resistance reading to the manufacturer’s specifications. If the resistance is outside the specified range, the ignition coil is likely faulty and needs to be replaced.
Replacing an ignition coil can be more complex than replacing a spark plug. It may require removing the engine shroud and other components. If you are not comfortable performing this repair, it is best to take the mower to a small engine repair shop.
Kill Switch Problems: Cutting Off the Ignition
The kill switch is a safety device that shuts off the engine when the operator releases the handle. A faulty kill switch can prevent the engine from starting, even if the other components of the ignition system are working properly.
The kill switch is typically located on the handle of the mower. Inspect the kill switch for any signs of damage or corrosion. Disconnect the kill switch wires and use a multimeter to test for continuity. When the kill switch is engaged (handle released), there should be continuity between the wires. When the kill switch is disengaged (handle held), there should be no continuity. If the kill switch is not functioning properly, it needs to be replaced.
Mechanical Issues: When the Engine Can’t Turn
Sometimes, the problem isn’t electrical or fuel-related, but mechanical. These issues can prevent the engine from turning over, making it impossible to start.
Low Compression: The Heart of the Engine
Compression is the pressure created inside the cylinder when the piston moves up and down. Low compression can be caused by worn piston rings, a damaged cylinder, or a leaky valve. Low compression will prevent the air-fuel mixture from igniting properly.
Testing compression requires a compression tester. Remove the spark plug and screw the compression tester into the spark plug hole. Pull the starter cord several times and observe the reading on the compression tester. The compression reading should be within the manufacturer’s specifications.
Low compression can be a sign of serious engine damage. Repairing low compression can be expensive and may require replacing the engine.
Blade Obstruction: A Simple Fix
The mower blade must be able to turn freely for the engine to start. If the blade is obstructed by grass, debris, or a foreign object, it can prevent the engine from turning over.
Inspect the blade area for any obstructions. Remove any grass, debris, or foreign objects that are blocking the blade. Make sure the blade is not bent or damaged. A bent blade can also cause the engine to vibrate excessively.
Recoil Starter Problems: The Pull Cord Mechanism
The recoil starter is the mechanism that allows you to manually start the engine by pulling the cord. A faulty recoil starter can prevent you from pulling the cord or can prevent the engine from turning over.
If the pull cord is difficult to pull, the recoil starter spring may be broken or damaged. The recoil starter mechanism may also be dirty or corroded. Disassemble the recoil starter and inspect the spring and other components. Clean the mechanism with a solvent and lubricate it with a light oil. If the spring is broken, it needs to be replaced.
Safety First: Prioritize Safe Practices
Before attempting any repairs on your lawn mower, it is important to prioritize safety.
- Disconnect the spark plug wire: This will prevent the engine from accidentally starting while you are working on it.
- Wear safety glasses: This will protect your eyes from debris and chemicals.
- Wear gloves: This will protect your hands from dirt, grease, and chemicals.
- Work in a well-ventilated area: This will prevent you from inhaling harmful fumes.
- Drain the fuel tank: This will prevent fuel spills and potential fire hazards.
Troubleshooting a lawn mower that won’t start can be a challenging but rewarding experience. By systematically checking the fuel system, ignition system, and mechanical components, you can often diagnose the problem and get your mower back in action. Remember to prioritize safety and consult the owner’s manual for specific instructions and recommendations for your mower model. If you are not comfortable performing the repairs yourself, it is always best to take the mower to a qualified small engine repair shop.
By carefully following the steps outlined in this guide, you’ll be well-equipped to tackle most common starting problems and keep your lawn looking its best.
Why does my lawn mower pull cord seem stuck and won’t budge?
If your pull cord feels completely jammed, the most likely culprit is a seized engine. This often occurs when the mower hasn’t been used for a while, allowing old fuel to gum up the carburetor or the cylinder to rust internally. Trying to force the cord could damage it or other engine components.
The best initial step is to check the oil level. If it’s low or empty, adding oil might free the engine. If oil is present and the cord remains stuck, try removing the spark plug and injecting a small amount of penetrating oil into the cylinder. Let it sit for several hours or overnight before gently attempting to pull the cord again. If it still won’t move, a more serious engine issue likely exists, requiring professional repair.
I can pull the cord, but the engine just won’t start. What could be the issue?
When the cord pulls freely but the mower refuses to start, the problem usually lies within the fuel, ignition, or compression systems. Start by checking the fuel supply. Ensure there’s fresh gasoline in the tank and that the fuel shut-off valve (if equipped) is open. Old or stale fuel is a common cause of starting problems.
Next, inspect the spark plug. Remove it and check for fouling (carbon buildup or wetness). Clean or replace the spark plug if necessary. Also, make sure the spark plug wire is securely attached. If the plug is clean and properly connected, use a spark plug tester to verify that it’s producing a spark when you pull the cord. No spark indicates an ignition system problem.
How can I tell if the fuel is the problem when my mower won’t start?
Fuel issues are extremely common with small engines, especially after periods of inactivity. A telltale sign is the smell of stale gasoline. If the fuel smells varnished or has a sour odor, it’s likely deteriorated and needs to be replaced. Also, observe the fuel filter (if visible) for any signs of blockage or sediment.
Another diagnostic step is to try priming the carburetor (if your mower has a primer bulb) or using starting fluid. If the mower starts briefly after priming or using starting fluid, it strongly suggests a fuel delivery problem. This could be a clogged carburetor, a faulty fuel pump, or a blocked fuel line.
What does a dirty or faulty spark plug look like, and how do I fix it?
A dirty spark plug typically appears black and sooty (carbon fouling) or wet with fuel. Carbon fouling indicates incomplete combustion, while a wet plug suggests the engine is being flooded with fuel. Either condition can prevent the plug from generating a spark, hindering ignition.
To fix a fouled spark plug, first, clean it with a wire brush or spark plug cleaner to remove any deposits. Check the gap between the electrode and ground electrode using a spark plug gap tool and adjust it to the manufacturer’s specifications. If the spark plug is severely damaged, cracked, or the electrode is worn, it’s best to replace it with a new one.
Could a dirty air filter prevent my lawn mower from starting?
Yes, a severely clogged air filter can definitely prevent a lawn mower from starting, or cause it to run poorly. The engine needs air to mix with the fuel for combustion. If the air filter is blocked with dirt and debris, the engine won’t receive enough air, leading to a rich fuel mixture that makes starting difficult.
Inspect the air filter regularly. If it’s paper-based, gently tap it to remove loose dirt. If it’s a foam filter, wash it with soap and water, then allow it to dry completely before oiling it lightly with air filter oil. If the filter is excessively dirty or damaged, replace it with a new one to ensure proper airflow to the engine.
What is a carburetor, and why does it sometimes cause starting problems?
The carburetor is a critical component responsible for mixing air and fuel in the correct ratio for combustion within the engine. Over time, especially if the mower is stored with fuel in the tank, the small passages and jets within the carburetor can become clogged with varnish and deposits from the fuel.
A clogged carburetor restricts fuel flow, leading to a lean fuel mixture (too much air, not enough fuel), which makes starting difficult or impossible. Symptoms of a carburetor problem include difficulty starting, rough idling, stalling, and poor engine performance. Cleaning or rebuilding the carburetor is often necessary to resolve these issues.
How can I prevent starting problems from recurring in the future?
Preventive maintenance is key to avoiding starting problems. Before storing your mower for the off-season, stabilize the fuel with a fuel stabilizer additive. This prevents the fuel from deteriorating and forming deposits in the fuel system. Alternatively, you can drain the fuel tank completely.
Regularly inspect and maintain the air filter, spark plug, and oil level. Change the oil according to the manufacturer’s recommendations. By following a consistent maintenance schedule, you can keep your lawn mower running smoothly and minimize the likelihood of starting problems when you need it most.