A lawn mower refusing to start is a common frustration for homeowners. Briggs & Stratton engines are widely used, and while reliable, they are not immune to issues. Understanding the potential causes and learning basic troubleshooting steps can save you time, money, and a trip to the repair shop. This guide will walk you through the most common reasons why your Briggs & Stratton mower might be stubbornly refusing to start.
Fuel System Issues: The First Suspect
Fuel is the lifeblood of any combustion engine. Problems within the fuel system are often the culprits behind a non-starting mower. Let’s examine the most frequent issues:
Old or Stale Fuel
Gasoline degrades over time, especially when exposed to air. Old fuel can become gummy and varnish-like, clogging fuel lines and carburetor jets. This makes it difficult, if not impossible, for the engine to draw fuel.
If your mower has been sitting idle for several months, the fuel is likely the problem. A telltale sign of stale fuel is a varnish-like smell emanating from the gas tank.
Solution: Drain the old fuel completely. Dispose of it properly at a local recycling center or hazardous waste facility. Refill the tank with fresh, high-quality gasoline. Consider adding a fuel stabilizer to prevent future degradation.
Clogged Fuel Line
The fuel line delivers fuel from the tank to the carburetor. This line can become clogged with debris, dirt, or the aforementioned gumming from stale fuel.
Solution: Disconnect the fuel line at both ends (tank and carburetor). Use a small length of wire or a fuel line cleaning kit to clear any obstructions. You might even use compressed air, blowing from the carburetor end back towards the tank. Be sure to do this in a well-ventilated area and wear eye protection. Replace the fuel line if it appears cracked, brittle, or significantly degraded.
Blocked Carburetor
The carburetor is responsible for mixing fuel and air in the correct ratio for combustion. A clogged carburetor is one of the most common reasons a Briggs & Stratton mower won’t start. Small jets and passages within the carburetor are easily blocked by debris from stale fuel or a dirty air filter.
Solution: Carburetor cleaning is essential. You have two main options:
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Carburetor Cleaner Spray: You can try spraying carburetor cleaner directly into the carburetor throat while attempting to start the engine. This might dislodge minor blockages.
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Carburetor Removal and Cleaning: This is the more thorough (and recommended) approach. Carefully remove the carburetor (refer to your mower’s service manual or online videos for specific instructions). Disassemble the carburetor and soak the parts in carburetor cleaner. Use small wires or carburetor cleaning tools to clear all jets and passages. Reassemble the carburetor and reinstall it on the engine. Many affordable carburetor replacement kits are available online if cleaning proves insufficient.
Faulty Fuel Cap
A seemingly insignificant component, the fuel cap plays a crucial role. It vents the fuel tank, allowing air to enter as fuel is consumed. If the vent is blocked, a vacuum can form in the tank, preventing fuel from flowing to the carburetor.
Solution: Try loosening or removing the fuel cap. Then, try starting the mower. If it starts, the fuel cap is likely the problem. You can try cleaning the vent hole on the cap or replace the cap altogether.
Spark Ignition System Issues: No Spark, No Start
The spark plug ignites the fuel-air mixture in the cylinder, initiating the combustion process. A malfunctioning spark ignition system will undoubtedly prevent the mower from starting.
Defective Spark Plug
The spark plug can become fouled with carbon deposits, oil, or fuel. A worn or damaged spark plug will not produce a strong enough spark to ignite the fuel-air mixture.
Solution: Remove the spark plug and inspect it. Look for cracks, excessive wear, or heavy deposits. Clean the spark plug with a wire brush or spark plug cleaner. Check the spark plug gap using a spark plug gap tool. Consult your mower’s manual for the correct gap setting. If the spark plug is damaged or heavily fouled, replace it. It is a good practice to replace the spark plug annually.
Faulty Ignition Coil
The ignition coil generates the high voltage needed to create a spark at the spark plug. A failing ignition coil may not produce enough voltage, resulting in a weak or non-existent spark.
Solution: Testing the ignition coil requires a spark tester. Attach the tester between the spark plug wire and the engine block. Crank the engine and observe the spark tester. A strong, consistent spark indicates a good ignition coil. A weak or absent spark suggests a faulty ignition coil that needs replacement. Consider consulting a qualified mechanic for proper testing and replacement of the ignition coil.
Kill Switch Problems
Most lawn mowers have a kill switch that grounds the ignition system, preventing the engine from starting when the bail lever is released. A faulty kill switch or a wiring problem in the kill switch circuit can prevent the engine from starting even when the bail lever is engaged.
Solution: Inspect the kill switch and its wiring for damage or loose connections. If you suspect a faulty kill switch, you can bypass it temporarily to see if the mower starts. Disconnect the wire leading to the kill switch. If the mower starts, the kill switch is the culprit. Replace the kill switch with a new one.
Air Intake Problems: Suffocating the Engine
The engine needs a proper air-fuel mixture to ignite. Restricting airflow starves the engine and leads to starting difficulties.
Clogged Air Filter
The air filter prevents dirt and debris from entering the engine. A dirty air filter restricts airflow, resulting in a rich fuel-air mixture that is difficult to ignite.
Solution: Remove the air filter and inspect it. If it is visibly dirty, clean it or replace it. Foam air filters can usually be cleaned with soap and water, then oiled lightly. Paper air filters should be replaced. Always check your mower’s manual for the recommended cleaning or replacement procedure for your specific air filter type.
Blocked Air Intake
Occasionally, debris such as grass clippings or leaves can block the air intake screen or the carburetor air intake.
Solution: Inspect the air intake screen and the carburetor air intake for any obstructions. Remove any debris that you find.
Mechanical Issues: Deeper Problems
While less common, mechanical problems can also prevent your Briggs & Stratton mower from starting.
Low Oil Level
Most Briggs & Stratton engines have a low-oil sensor that prevents the engine from starting when the oil level is too low. This is to protect the engine from damage.
Solution: Check the oil level using the dipstick. If the oil level is low, add the appropriate type and amount of oil, as specified in your mower’s manual.
Engine Compression Problems
Engine compression is essential for proper combustion. Worn piston rings, a damaged cylinder, or a leaking valve can result in low compression, making it difficult or impossible to start the engine.
Solution: Checking engine compression requires a compression tester. Insert the tester into the spark plug hole and crank the engine. A healthy engine should have a compression reading within the range specified in the mower’s manual. Low compression indicates a serious mechanical problem that may require professional repair.
Sheared Flywheel Key
The flywheel key is a small piece of metal that connects the flywheel to the crankshaft. If the mower blade strikes a solid object, the flywheel key can shear, causing the timing to be off and preventing the engine from starting.
Solution: Inspecting the flywheel key requires removing the flywheel. If the key is sheared, it will need to be replaced. This repair is best left to a qualified mechanic, as it involves working with rotating engine components.
Starting System Issues: Beyond the Engine
Sometimes, the problem isn’t directly with the engine itself, but with the starting mechanism.
Pull Cord Problems
For recoil start mowers, the pull cord mechanism can fail. The cord may be broken, the recoil spring may be damaged, or the pawls that engage the flywheel may be worn.
Solution: Inspect the pull cord for fraying or breakage. If the cord is broken, replace it. If the recoil spring is weak or broken, the entire recoil starter assembly may need to be replaced. Check the pawls for wear and replace them if necessary.
Electric Starter Problems
For electric start mowers, the starter motor, solenoid, or battery can be the cause of the problem.
Solution: First, ensure the battery is fully charged. If the battery is good, check the starter solenoid. You can try jumping the solenoid terminals with a screwdriver (carefully!). If the engine cranks, the solenoid is faulty and needs replacement. If the engine still doesn’t crank, the starter motor itself may be faulty and require replacement.
Troubleshooting Steps Summary
Here’s a summary of the steps to take when your Briggs & Stratton mower won’t start:
- Check the fuel: Is it fresh? Drain and replace if necessary.
- Inspect the fuel line: Is it clear and unobstructed?
- Clean the carburetor: A clogged carburetor is a common culprit.
- Check the spark plug: Is it clean and gapped correctly? Replace if necessary.
- Test the ignition coil: Is it producing a strong spark?
- Examine the air filter: Is it clean and allowing adequate airflow?
- Check the oil level: Is it within the correct range?
- Look for mechanical problems: Low compression or a sheared flywheel key may require professional attention.
- Examine the starting system: Check pull cord for functionality or electrical starter for battery issues.
Preventative Maintenance: Avoiding Future Headaches
Preventative maintenance is key to keeping your Briggs & Stratton mower running smoothly and avoiding starting problems.
- Use fresh fuel and add fuel stabilizer: Prevent fuel degradation during storage.
- Clean or replace the air filter regularly: Ensure proper airflow.
- Change the oil regularly: Keep the engine lubricated and prevent wear.
- Inspect and clean the spark plug annually: Maintain optimal spark performance.
- Store the mower properly: Protect it from the elements.
- Sharpen or replace the mower blade regularly: A sharp blade reduces strain on the engine.
- Follow the manufacturer’s recommendations: Refer to your mower’s manual for specific maintenance schedules and procedures.
By following these troubleshooting steps and implementing a regular maintenance schedule, you can keep your Briggs & Stratton mower starting reliably and performing optimally for years to come. Remember safety first when working on any machinery. If you are uncomfortable with any of these procedures, it is always best to consult a qualified mechanic.
Why is my lawn mower engine cranking but not starting?
A common reason for a cranking but non-starting Briggs & Stratton mower is a lack of fuel or a fuel delivery problem. Check the fuel tank to ensure it’s adequately filled with fresh gasoline. Older fuel can degrade and lose its combustibility, especially if left sitting over the winter. Also, inspect the fuel line for any kinks, cracks, or blockages that might be preventing fuel from reaching the carburetor. A clogged fuel filter can also restrict fuel flow.
Another possible cause is a faulty spark plug. Even if the engine is cranking, a weak or non-existent spark won’t ignite the fuel mixture in the cylinder. Remove the spark plug and inspect it for signs of damage, such as a cracked insulator or excessive carbon buildup. Clean or replace the spark plug as needed. You can use a spark plug tester to verify that the plug is producing a strong, consistent spark.
What should I do if my lawn mower won’t start and the pull cord is hard to pull?
A hard-to-pull pull cord usually indicates a problem with the engine’s compression release system or the engine being hydraulically locked. The compression release system is designed to make the engine easier to start by relieving some of the pressure in the cylinder during the initial pull. If this system fails, the engine will be much harder to turn over.
Hydraulic lock occurs when liquid (usually oil or gasoline) enters the combustion chamber, preventing the piston from moving freely. This can happen if the mower has been stored improperly or if it has been tilted excessively. To resolve hydraulic lock, remove the spark plug and try to pull the cord again. The liquid should be expelled from the spark plug hole. If the problem persists, professional service might be needed.
How do I clean or replace a dirty air filter on my Briggs & Stratton mower?
Cleaning or replacing a dirty air filter is a simple maintenance task that can significantly improve your mower’s performance. Locate the air filter housing, usually on top of or to the side of the engine. Open the housing and remove the air filter. If it’s a foam filter, wash it with mild soap and water, squeeze out the excess water, and allow it to dry completely before re-oiling it lightly with air filter oil.
If the air filter is a paper filter, you can try tapping it gently to remove loose dirt and debris. However, if the filter is heavily soiled or damaged, it should be replaced. Ensure the replacement filter is the correct type for your mower model. Once the filter is clean or replaced, reinstall it in the housing and close the housing securely.
What is the purpose of the carburetor on my lawn mower and how do I troubleshoot it?
The carburetor’s primary function is to mix air and fuel in the correct ratio for combustion. It draws fuel from the fuel tank and combines it with air before delivering the mixture to the engine’s cylinder. A malfunctioning carburetor can cause starting problems, rough running, or stalling.
Common carburetor issues include clogs from old fuel, gum deposits, or debris. To troubleshoot, start by inspecting the carburetor for visible dirt or damage. If possible, carefully remove the carburetor and clean it thoroughly with carburetor cleaner. Pay close attention to the small jets and passages, ensuring they are clear. If cleaning doesn’t resolve the issue, the carburetor might need to be rebuilt or replaced.
What are some common problems with the ignition system that can prevent my mower from starting?
The ignition system generates the spark that ignites the air-fuel mixture in the engine’s cylinder. Common ignition system problems include a faulty spark plug, a damaged ignition coil, or a malfunctioning kill switch. As mentioned earlier, a weak or non-existent spark plug will prevent combustion.
The ignition coil is responsible for generating the high voltage needed to create the spark. If the coil is damaged or failing, it might not produce enough voltage. The kill switch is a safety feature that grounds the ignition system, preventing the engine from starting. A faulty kill switch can prevent the mower from starting even if all other components are working correctly. Check the wiring and connections to ensure they are secure and free from corrosion.
Why is my lawn mower only running for a few minutes before stalling?
A mower that runs briefly and then stalls often indicates a fuel delivery problem. This could be due to a partially clogged fuel filter, a restricted fuel line, or a venting issue in the fuel tank cap. A partially clogged fuel filter or restricted fuel line can initially provide enough fuel to start the engine, but the flow diminishes quickly, causing the engine to stall.
Another possibility is a venting problem in the fuel tank cap. The fuel tank needs to be properly vented to allow air to replace the fuel as it’s used. If the vent is blocked, a vacuum can form in the tank, preventing fuel from flowing to the carburetor. Try loosening the fuel cap slightly to see if this resolves the issue. Also, a dirty carburetor bowl can cause fuel starvation after initial startup.
What is the low oil sensor on my Briggs & Stratton mower and how does it affect starting?
The low oil sensor is a safety device designed to prevent the engine from running when the oil level is too low. It works by grounding the ignition system when the oil level drops below a certain threshold, effectively shutting off the engine. This protects the engine from severe damage caused by running without adequate lubrication.
If the low oil sensor is malfunctioning, it can prevent the mower from starting even if the oil level is sufficient. This can happen if the sensor is damaged or if the wiring is faulty. Try disconnecting the low oil sensor to see if the mower starts. However, be aware that disabling the sensor will remove the protection it provides, so it’s important to ensure the oil level is checked regularly and maintained at the proper level if you choose to operate the mower without the sensor.