Troubleshooting a Briggs and Stratton Lawn Mower That Won’t Start in 5 Simple Steps

It can be annoying when a lawn mower won’t start, especially when the grass is overgrown. Although Briggs & Stratton lawn mowers are renowned for their toughness and dependability, problems can arise with any mechanical equipment.

If your Briggs & Stratton lawnmower doesn’t start, rest assured that there are a few possible reasons to consider.

In this article, you will learn how to fix each of the most common causes of lawnmowers not starting.  

How a Lawn Mower Engine Works

Understanding the operation of your lawn mower’s engine is a crucial step before diving into troubleshooting. Most Briggs & Stratton lawnmowers are equipped with a four-stroke engine, which functions through four key processes: intake, compression, power, and exhaust.

1. Intake: The engine draws in air and fuel.

2. Compression: The piston compresses the air-fuel mixture.

3. Power: A spark ignites the mixture, creating an explosion that drives the piston.

4. Exhaust: The engine expels the burnt gases through the exhaust.

If any part of this process is disrupted, the engine may fail to start. The most common issues involve fuel, air, spark, and compression, which we’ll explore in detail.

Step 1: Check the Fuel System

The fuel system is often the reason a lawn mower does not start. Issues such as stale fuel, clogged fuel lines, or carburetor problems can prevent fuel from reaching the engine or combusting properly.

1. Fuel Quality: The fuel may have gone stale if your lawn mower has been unused for a while. Gasoline degrades over time, leading to poor engine performance or a complete failure to start.

Solution: Drain the old fuel from the tank and carburettor and replace it with fresh gasoline. Using fuel stabilizers is also advisable for storing the mower for extended periods.

2. Fuel Line and Filter: Dirt and debris can clog the fuel line or filter, restricting fuel flow to the engine.

Solution: Inspect the fuel line for blockages and the fuel filter for signs of dirt. Replace the filter if necessary and clean the fuel line.

3. Carburetor Issues: The carburettor mixes fuel with air before sending it to the engine. Over time, it can become clogged with dirt or residue from old fuel.

Solution: Clean the carburettor using a carburettor cleaner. If the carburettor is severely clogged or damaged, consider rebuilding or replacing it.

Step 2: Inspect the Air Filter

An engine needs a proper air-fuel mixture to start and run efficiently. A blocked air filter can disrupt this balance, leading to starting issues.

1. Clogged Air Filter: A dirty or clogged air filter prevents sufficient air from entering the carburettor, leading to a rich fuel mixture that can flood the engine.

Solution: Remove the air filter and inspect it. If it’s dirty, clean it according to the manufacturer’s instructions or replace it with a new one.

2. Air Filter Type: These can be cleaned with soap and water but must be thoroughly dried before reinstallation. If your lawn mower uses Paper filters, they should be replaced rather than cleaned, as washing them can damage the filter material.

Step 3: Check the Spark Plug

The spark plug ignites the air-fuel mixture in the engine. If the spark plug is faulty, the engine won’t start.

1. Spark Plug Condition: Over time, spark plugs can become fouled with carbon deposits or oil, or they may wear out.

Solution: Remove the spark plug and inspect it. If it’s covered in black soot oily residue or shows signs of wear, clean it or replace it with a new one. Ensure the spark plug gap is set to the manufacturer’s specifications.

2. Spark Plug Connection: A loose or disconnected spark plug wire can prevent the engine from starting.

Solution: Check that the spark plug wire is securely connected to the plug. If it’s loose, push it back on until it clicks into place.

Step 4: Ensure Proper Compression

An engine requires adequate compression to operate correctly. If compression is low, the engine may struggle to start or may not start at all.

1. Compression Issues: Over time, the piston rings or cylinder walls can wear out, leading to a loss of compression.

Solution: Perform a compression test using a compression gauge. If the compression is low, it may indicate worn piston rings, a damaged cylinder, or a blown head gasket. These issues typically require professional repair.

2. Valves and Timing: The intake and exhaust valves must open and close at the correct times to ensure proper compression. If the valves are damaged or out of sync, the engine may not start.

Solution: Valve issues often require adjustments or repairs by a qualified technician.

Step 5: Additional Troubleshooting Steps

If the fuel, air, spark, and compression systems are all functioning correctly and your Briggs & Stratton lawn mower still won’t start, there are a few additional areas to check.

1. Safety Switches: Most lawnmowers have safety switches that prevent the engine from starting under certain conditions, such as when the blade is engaged or the handle is not held down.

Solution: Check the safety switches to ensure they are working correctly. If a switch is faulty, it may need to be replaced.

2. Battery and Electrical System: If your mower has an electric start, a weak or dead battery could prevent it from starting.

Solution:

1. Test the battery with a multimeter.
2. If it’s low, recharge or replace it.
3. Check the electrical connections for corrosion or loose wires.

3. Choke and Throttle Position: Starting issues can arise if the choke or throttle is incorrectly set.

Solution: Ensure the choke is in the correct position for starting (typically fully on) and the throttle is set to the recommended position.

Preventative Maintenance Tips

Regular maintenance is not just good practice; avoiding future issues with your Briggs & Stratton lawn mower is critical. By following these tips, you can take proactive steps to keep your mower in top shape and prevent potential starting issues.

1. Regularly Change the Oil: Old or dirty oil can cause engine problems. Change the oil at least once per season or after every 25-50 hours of use.

2. Keep the Air Filter Clean: Check and clean the air filter regularly and replace it as needed. A clean air filter ensures optimal engine performance.

3. Use Fresh Fuel: Always use fresh gasoline, and add a fuel stabilizer if storing the mower for extended periods. This prevents fuel degradation and carburettor gumming.

4. Inspect and Replace Spark Plugs: Check the spark plug at the beginning of each season and replace it if it shows signs of wear or fouling.

5. Store the Mower Properly: At the end of the mowing season, drain the fuel, clean the mower, and store it in a dry, sheltered area. Proper storage prevents issues like rust, corrosion, and fuel degradation.

In Summary 

When your Briggs & Stratton lawn mower doesn’t start, it’s essential to systematically troubleshoot the potential causes, from the fuel system to the ignition and beyond. By following the steps outlined in this guide, you can diagnose and fix most starting issues. Regular maintenance, including checking the fuel, air filter, spark plug, and compression, will help ensure your lawn mower starts reliably season after season. If you encounter more complex problems, such as compression issues or damaged valves, it may be necessary to seek professional repair. Remember, a well-maintained lawn mower starts quickly and provides better performance and a longer lifespan.