How do I troubleshoot & repair common engine problems?

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Engine Won’t Start

Engine starting problems have a few common causes, especially if you’re using your 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.

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.

Prevent this problem in advance through proper lawn mower & outdoor power equipment storage. Using fuel stabilizer will keep your gas from creating engine problems.

Step 2: Clean the Carburetor

Carburetor problems cause engines not to start. The carburetor regulates how air and fuel move through the engine to power your equipment. If it is dirty, that can cause poor engine performance or starting problems.

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 prevent a spark. These can range from a faulty spark plug lead, shorted kill switch or flywheel key damage.

To test and fix, check out our Engine Ignition Systems FAQ or reach out to your local dealer for advanced repair help.

Step 4: Check the Valves & Compression System

Air, Fuel, Compression, and Spark is crucial to engines powering outdoor power equipment. The compressions system is made up of valves, Piston(s), Cylinder(s) and rings that control how the air and fuel vapors move through the engine. Valves allow the fresh air/fuel charge in and out of the cylinder. The up and down movement of the piston in the cylinder helps draw the fresh air/fuel mixture in passed the intake valve and push the burned air/fuel mixture out of the cylinder through the exhaust valve. The rings seal the air/fuel mixture while ignition (spark) is occurring.

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 complete compression system check with a Leakdown tester (Part # 19545). 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.

Engine Running Poorly?

Use this simple Q&A to troubleshoot engine problems you may experience with your outdoor 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.

Is your fuel fresh?
Stale, untreated gas begins to break down after about a month. Drain the gas from your 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 before 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)

Engines Smoking

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?
You need to perform a Carburetor Adjustment.

Is the air filter dirty / plugged?
Clean or replace the air filter.

Engine Overheating

Is the engine dirty?
Follow instructions for safely cleaning & removing debris from 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 the fuel mixture too lean?
You can determine if your air-fuel mixture is off by checking the state of your carburetor. Use this Carburetor Adjustment FAQ as a guide.

Is there a leaky gasket?
All mounting hardware is tight and gaskets are checked for proper sealing

Is the fuel tank vent or fuel tank screen plugged?
Clean the fuel tank vent and screen.

Engine Knocking

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).

Spark Plug Fails When In Use

Is the spark plug fouled?
Clean spark plugs where applicable (Follow instructions for checking & changing spark plugs).

Is the spark plug faulty or gap incorrect?
Replace the spark plug or adjust the spark plug gap (see Spark Plug Gap FAQ).

Are your carburetor settings correct?
Check your engine’s carburetor settings. Find the proper carburetor settings and step-by-step directions for Carburetor Adjustment. for old engines, current engine carburetors are not adjustable.

Is the valve spring weak?

Check that the valve spring still has tension.

To access this, you’ll have to remove the muffler 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 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).

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