Having engine problems? Use this comprehensive guide when troubleshooting issues with your lawn mower, snow blower or other outdoor power products - whether your product won’t start, is stalling, surging or running rough.
How do I troubleshoot & repair common small engine problems?
WARNING: Always read the engine and equipment manual(s) before starting, operating, or servicing your engine or equipment to avoid personal injury or property damage. See an authorized dealer or contact Briggs & Stratton if you are unsure of any procedure or have additional questions. Find all Engine Safety Warnings
Engine starting problems have a few common causes, especially if you’re using your lawn mower or outdoor power product after it’s been stored for the winter or off-season.
Safety Tip: ALWAYS remove / disconnect the spark plug before performing engine repair.
Step 1: Check Your Fuel
Do you have fresh, clean fuel in the tank? If it’s empty, fill it up and go! If it’s full, check that the fuel shut-off valve is open and that it is clean.
Fuel needs to be stored in a suitable container . Stale fuel, dirt and debris are the most common cause of outdoor power equipment not starting properly. If you store equipment with untreated gas in the tank, it can lead to engine damage.
Step 2: Clean the Carburetor
Carburetor Problems Cause Mower Engines Not To StartThe carburetor regulates how air and fuel move through the engine to power your equipment. If the carburetor is dirty, that can cause poor engine performance or starting problems.
>> Follow these steps for cleaning carburetors
>> Follow these steps for carburetor rebuild
Step 3: Check the Spark Plug & Possible Ignition Problems
Disconnected, dirty or fouled spark plugs are common causes for engines that won’t start. Spark plugs typically need to be replaced every season or 25 hours of use. You should also check that the spark plug gap is set properly.
>> Follow this guide on checking and replacing spark plugs
If your spark plugs look good, problems with your ignition system can also preventing a spark. These can range from a faulty spark plug lead, shorted kill switch or flywheel key damage.
Step 4: Check the Valves & Compression System
Air-fuel compression is crucial to engines powering lawn mowers and outdoor power equipment. The compressions system is made up of valves, piston, cylinders and rings that control how the air and fuel vapors move through the engine. Valves let air in (the intake valve) and out (the exhaust valve), pistons move back and forth pushing the air-fuel mixture to the ignition system and the piston rings keep it all sealed up tight.
If there isn’t proper valve clearance or there’s a leak, this can cause compression problems that keep an engine from starting. You can perform a compression system with a leak down tester. If you don’t have one of these, we recommend visiting your Briggs & Stratton repair dealer to perform the test and check that these components are in good shape.
Use this simple Q&A format list to troubleshoot small engine problems you may experience with your lawn mower, snow blower or other power equipment.
Engine Stalling, Surging or Running Rough
When your engine starts and stalls, it is often due to standard maintenance problems. Prevent stalling problems before they start with a tune-up kit. See “Why My Engine Won’t Start” section above or use the Q&A guide below.
Is your fuel fresh?
Stale, untreated gas begins to break down after about a month. Drain the gas from your lawn mower our outdoor power equipment, then replace with fresh gas and fuel stabilizer to extend the life of your fuel.
Is the air filter dirty / plugged?
Clean or replace the air filter.
Is the spark plug fouled?
Clean spark plugs where applicable (Follow instructions for checking and changing spark plugs).
Is your oil fresh?
Check your oil level and appearance every time you use your engine while it is cold. Your oil needs to be changed every 25 hours of use or season. (See Checking and Changing Mower Oil)
The new EXi engines series from Briggs & Stratton makes lawn mower oil maintenance easier than ever with Just Check & Add Engines.
Is the engine emitting white / blue smoke?
This means your engine burning oil. (see Engine emits white/blue smoke while running).
Is the engine emitting black smoke?
Could be caused by a dirty air filter, flooded carburetor, and/ or bad fuel.
Is the air filter dirty / plugged?
Clean or replace the air filter.
Is the engine dirty?
Follow instructions for safely cleaning & removing debris from small engines.
Is the oil level low?
Add oil to the engine. NOTE: Never add oil to the gasoline for a four-stroke engine (see Checking & Changing Oil).
Are any shrouds or cooling fins missing or broken?
Install new parts as needed. Reference your repair manual, available for purchase.
Is there a leaky gasket?
This is another common carburetor problem associated with overheating engines. Learn how to check and replace the gasket (see Lawn Mower Carburetor Rebuild FAQ).
Is the fuel tank vent or fuel tank screen plugged?
Clean the fuel tank vent and screen.
Does the combustion chamber contain excess carbon?
Carbon deposits can form on your combustion chamber. If you see any, simply clean carbon from the piston and head (see Removing Engine Carbon Deposits).
Is the flywheel loose?
Inspect the flywheel and key; replace as needed (see Inspecting the Flywheel & Key).
Is the spark plug lead faulty?
Test the lead with a spark tester, then test the engine (see Servicing Spark Plugs).
Engine, blade, or attachment could also be loose.
Spark Plug Fails When In Use
Check that the valve spring still has tension.
To access this, you’ll have to remove the muffler, crankcase and other components blocking the valve chamber. Then, remove the cylinder head bolts (label for easy re-installation)
Adjust the jaws of the valve spring compressor until they touch the top and bottom of the valve chamber
Push the tool in to compress the spring and tighten the jaws
Remove the retainers and lift out the valves , compressors and springs
If you find weak springs, replace them based on your small engine’s specifications. These can be found in your operator’s manual.
Is the valve clearance set incorrectly?
If your valve spring is still working well, check the clearance. Valves that stick or have leaks can cause an engine to stop running. Adjust the valve clearance to recommended settings (see your operator’s manual).
Shop Related Maintenance Parts
Learn how to properly and safely use, troubleshoot, and maintain your lawn mower, tractor, snow blower, and other lawn and garden equipment.
Learn about the latest products by Briggs & Stratton, step-by-step instructions on how to locate your lawn mower engine model number, and more!