You pull out your trusty Briggs and Stratton lawn mower after months of sitting, prime it, pull the cord… and nothing happens. Don’t worry—this is one of the most common mower problems, especially after winter, and it’s usually easy to fix yourself. Let’s walk through the top reasons your Briggs and Stratton mower won’t start after storage (or after sitting for a few weeks), and what to do about each one.
Quick Picks: Most Common Reasons a Briggs & Stratton Mower Won’t Start After Storage
- Old or Stale Fuel: Fuel left in the tank or carburetor can break down and prevent starting.
- Gummed-Up Carburetor: Old fuel turns to varnish and clogs tiny jets and passages inside the carburetor.
- Fouled or Old Spark Plug: Plugs can corrode or become coated with deposits after sitting.
- Clogged Air Filter: Dust or insects may block the filter, starving the engine of air.
- Low or Dirty Oil: Some Briggs engines have oil-level sensors—low oil means no start.
- Dead Battery (for electric start): Batteries lose charge over time and may need a recharge or replacement.
- Stuck Float or Needle Valve: In the carburetor, these can stick from dried fuel, blocking flow.
- Rodent Nests or Debris: Mice and bugs sometimes build nests in the engine bay or air intake during storage.
Buyer’s Guide: What You’ll Need for a Spring Start-Up
- Fresh unleaded petrol (gasoline)
- Carburetor cleaner spray
- Spark plug socket and wrench
- Replacement spark plug and air filter
- Battery charger or new battery (if electric start)
- Oil and oil pan (for changing old oil)
- Work gloves and safety glasses
- Rags or shop towels
Step-by-Step: How to Fix a Briggs and Stratton Mower That Won’t Start After Storage
1. Empty Old Fuel and Add Fresh Gas
- Use a siphon or carefully tilt the mower to drain any fuel left in the tank and carburetor.
- Fill with fresh, clean gasoline—never more than 30 days old.
2. Inspect and Replace the Spark Plug
- Remove the spark plug and look for black, oily, or corroded electrodes.
- Clean with a wire brush or replace with a new, correctly gapped plug.
- Make sure the plug wire is firmly attached.
3. Clean or Replace the Air Filter
- Remove and inspect the air filter. If dirty, dusty, or packed with debris, replace it.
- A clean air filter ensures proper airflow for easier starting.
4. Charge or Replace the Battery (Electric Start Models)
- If your mower uses a battery, charge it overnight or replace it if it won’t hold a charge.
- Clean the battery terminals and check all electrical connections.
5. Clean the Carburetor
- If the mower still won’t start, remove the air filter and spray carburetor cleaner into the carburetor intake.
- Try starting the engine. If it runs for a second, the carburetor is likely gummed up. For persistent issues, remove and fully clean or rebuild the carburetor.
6. Change the Oil
- Old oil can get thick and sludgy. Drain it and refill with fresh oil as recommended in your manual.
- Low or dirty oil can trigger a shutoff sensor and block starting.
7. Check for Debris and Rodent Damage
- Inspect around the engine, under the shroud, and in the air intake for nests, chewed wires, or packed dirt.
- Clear out all debris and repair any damaged wires or hoses.
Comparison Table: Briggs and Stratton Mower Starting Problems & Solutions
| Problem | Solution | Difficulty | Parts Needed |
|---|---|---|---|
| Old/Stale Fuel | Drain and add fresh gasoline | Easy | Gasoline |
| Fouled Spark Plug | Clean or replace plug | Easy | Spark plug |
| Dirty Air Filter | Replace filter | Easy | Air filter |
| Dead Battery | Charge or replace battery | Easy | Battery, charger |
| Gummed-Up Carburetor | Clean carburetor | Easy-Medium | Carb cleaner |
| Old/Dirty Oil | Change oil | Easy | Oil |
| Rodent/Debris Blockage | Remove nests, repair wires | Easy | — |
| Stuck Float/Needle | Clean/rebuild carburetor | Medium | Carburetor kit |
Frequently Asked Questions
Why does my Briggs and Stratton only start with starting fluid?
This means fuel isn’t reaching the engine—usually a gummed carburetor or stuck float valve. Clean or rebuild the carburetor.
Should I always drain fuel before storage?
Yes! Running the mower dry or draining the tank and carb before storage prevents 90% of post-storage starting issues.
How often should I change the spark plug and air filter?
Replace at least once per season, or more often if you mow in dusty conditions.
Can bad oil prevent my Briggs mower from starting?
Low or very dirty oil can trigger safety shutoff sensors and make the engine harder to turn over—always check oil before starting after storage.
Conclusion
If your Briggs and Stratton lawn mower won’t start after storage, check for old fuel, a dirty carburetor, fouled plug, air filter, and low oil. Most problems are quick fixes you can handle yourself, so you’ll be back to mowing in no time—and with regular maintenance, your Briggs mower will last for years!