Briggs & Stratton engines are famous for their reliability, but even the best lawn mowers can refuse to start when you need them most. Whether you have a classic walk-behind, self-propelled, or riding mower powered by a Briggs & Stratton engine, starting issues are a common headache for homeowners. Fortunately, most causes are easy to diagnose and repair. This complete guide covers all the top reasons your Briggs & Stratton mower won’t start—and how you can fix it fast.
1. Why Won’t My Briggs and Stratton Mower Start? Quick-Check List
- Old or stale gasoline in the tank or carburetor
- Dirty, fouled, or damaged spark plug
- Clogged air filter
- Low oil level or dirty oil (many B&S engines have low-oil shutdown)
- Carburetor problems
- Battery issues (for electric start or riding mowers)
- Safety switches not engaged
- Mechanical obstructions (blade jam, deck clogs)
2. Initial Troubleshooting Steps
Before diving into deeper repairs, always rule out the simple stuff. Briggs & Stratton engines are designed to be user-friendly, so check the following first:
- Fuel: Is the tank filled with fresh gasoline? Old fuel (over 30 days) can cause hard starting or no start.
- Oil: Check the dipstick. Add or change oil if it’s low or dirty. Many modern B&S engines won’t start with low oil.
- Spark plug: Make sure the spark plug wire is firmly attached. Remove and inspect the plug for black soot, rust, or cracks.
- Air filter: Remove and inspect the filter. Clean or replace if dirty or clogged.
- All controls and safety levers engaged? Squeeze the bail/bar, sit on the seat (riding mowers), and ensure the parking brake is on.
- Battery: For electric start mowers, check that the battery is charged and terminals are clean.
3. Fuel System Problems: The #1 Culprit
Briggs & Stratton engines are very sensitive to old fuel. Here’s how to check the entire fuel system:
- Stale gasoline: Drain the tank and carburetor bowl. Refill with fresh gas.
- Water in the fuel: If you see a cloudy appearance or droplets at the bottom of the tank, drain and refill completely.
- Blocked fuel filter: Replace if dirty.
- Clogged fuel line: Inspect and replace cracked or collapsed lines.
- Fuel shutoff valve: If equipped, ensure it’s open.
Tip: Always use a fuel stabilizer if storing your mower for more than a month.
4. Spark Plug & Ignition Issues
Even the best Briggs & Stratton engine won’t start without a strong spark. Here’s how to check:
- Remove the spark plug: Look for carbon, oil fouling, or worn electrode. Replace if in doubt.
- Check the gap: Use a feeler gauge. Briggs & Stratton recommends a gap of 0.030” (0.76mm) for most engines.
- Test for spark: Reconnect the plug wire, ground the plug body on the engine, and pull the starter cord. Look for a blue spark.
- No spark? Try a new plug, then inspect the ignition coil or flywheel key if needed.
5. Air Filter & Air Intake
- Remove the air filter cover: Briggs & Stratton mowers typically use either foam or paper filters.
- Clean foam filters with soapy water, dry, and lightly oil before reinstalling.
- Replace paper filters if dirty or discolored.
- Briefly try starting with the filter removed: If it fires up, replace the filter.
6. Carburetor Problems: Cleaning & Adjustment
Gummed-up carburetors are a classic Briggs & Stratton no-start problem—especially after winter storage.
- Spray carburetor cleaner directly into the intake. If the engine fires and stalls, your carb needs deeper cleaning.
- Remove and clean the carburetor: If you’re comfortable, take it off and clean all jets and passages. Replace gaskets as needed.
- Check the primer bulb and fuel lines for cracks or leaks.
- Consider a carburetor rebuild kit if problems persist. Many are inexpensive and easy to install.
7. Mechanical & Safety Switch Issues
- Blade engagement: For safety, many B&S mowers won’t start if the blade is engaged. Make sure it’s fully disengaged.
- Seat, brake, and bail switches: Check that all safety switches are in their proper position. Replace faulty switches or wiring as needed.
- Blade jammed or debris under deck: Always disconnect the spark plug, then check under the deck for sticks, rocks, or grass buildup.
8. Battery and Electric Start Troubles (If Equipped)
- Test battery voltage: Should read at least 12.4 volts. Charge or replace if low.
- Clean battery terminals: Corrosion can block current. Use a wire brush.
- Listen for clicks: Clicking but no crank usually means a bad solenoid, starter, or weak battery.
- Inspect wiring: Make sure all wires are tight, undamaged, and connected to the correct terminals.
9. Flooded Engine: What to Do
- If the spark plug is wet or you smell gas, your engine might be flooded.
- Let the mower sit for 10–15 minutes to evaporate excess fuel.
- With the spark plug removed, pull the starter cord a few times to clear fuel from the cylinder.
- Dry and reinstall the spark plug, then try starting with no choke.
10. Advanced: Compression, Flywheel Key, & Internal Issues
- Low compression: Rare, but a worn cylinder or valves will prevent starting. A compression test (over 60 psi is ideal) may be needed.
- Sheared flywheel key: If your mower hit something hard, the flywheel key can shear, throwing off timing. This requires partial disassembly.
- Worn starter recoil assembly: For pull-start models, replace if the cord won’t retract or grip.
11. Seasonal & Preventive Maintenance for Briggs & Stratton Engines
- Change oil, spark plug, and air filter at least once per mowing season.
- Drain old fuel before winter or use a stabilizer.
- Keep the carburetor and air filter area clean after every mow.
- Store your mower in a dry place, out of the rain and damp.
12. Frequently Asked Questions (FAQ)
Why does my Briggs & Stratton mower crank but not start?
Most likely, the problem is with fuel, spark, or air—often old gasoline, a dirty spark plug, or a clogged carburetor. Work through the troubleshooting steps above.
How do I clean the carburetor on my Briggs & Stratton engine?
Remove the air filter and spray carburetor cleaner into the intake. For deeper cleaning, remove the carburetor, disassemble, and clean all jets and passages with carb cleaner and compressed air.
What spark plug does a Briggs & Stratton mower use?
Most B&S engines use an RJ19LM or J19LM spark plug with a 0.030” gap, but always check your engine’s manual.
What oil should I use in my Briggs & Stratton engine?
SAE 30 is common for most walk-behind mowers in warmer climates. Synthetic 5W-30 works well for wider temperature ranges. Always check your manual.
My mower still won’t start—should I call a repair shop?
If you’ve tried all the steps above and your Briggs & Stratton engine still won’t start, it may be time for professional help. Persistent issues could mean internal problems or advanced electrical faults.
13. Conclusion: Get Your Briggs & Stratton Mower Running Strong
A Briggs & Stratton mower that won’t start is almost always caused by something simple—old gas, a dirty spark plug, a clogged filter, or a carburetor in need of cleaning. With this troubleshooting guide, you can confidently diagnose and fix most problems at home. For major mechanical or electrical issues, your local small engine repair shop is ready to help.
With the right care, your Briggs & Stratton mower will deliver years of reliable performance—and keep your lawn looking sharp all season long!