It’s frustrating — you pull the cord or push the button, your lawn mower fires up, and then seconds later… it dies. Whether it’s a gas or electric mower, this issue is one of the most common problems homeowners face. The good news? In most cases, it’s fixable with simple troubleshooting and maintenance.
In this guide, we’ll explain why your lawn mower starts but won’t stay running, how to fix it, and what to check depending on your mower brand — including Honda, Craftsman, Toro, Husqvarna, Troy-Bilt, and John Deere.
🔍10 Causes Why a Lawn Mower Starts but Won’t Stay Running
Before diving into brand specifics, let’s cover the universal causes behind this problem.
1. Dirty or Clogged Carburetor
If your mower runs for a few seconds then stalls, a dirty carburetor is the prime suspect. Old gasoline can gum up the carburetor, preventing the proper fuel-air mixture needed for combustion.
Fix:
- Drain old fuel and clean the carburetor with a carb cleaner spray.
- For severe buildup, remove and soak the carburetor or use a rebuild kit.
👉 Tip: Use fuel stabilizer if you store your mower over the winter to prevent carb gumming.
2. Old or Stale Gasoline
Gasoline older than 30 days begins to degrade. Ethanol in the fuel attracts moisture, leading to poor combustion or stalling after startup.
Fix:
- Drain and replace with fresh fuel.
- Use ethanol-free or high-quality gas.
3. Dirty Air Filter
A clogged air filter restricts airflow, causing the engine to run rich (too much fuel, not enough air). This imbalance makes the mower stall shortly after starting.
Fix:
- Remove the air filter and inspect it.
- Tap out debris or replace if it’s dark or oily.
4. Blocked Fuel Line or Fuel Filter
Sediment and rust can block fuel flow to the carburetor, starving the engine.
Fix:
- Check fuel lines for cracks or clogs.
- Replace the inline fuel filter if it’s dirty or hasn’t been changed in a while.
5. Faulty Spark Plug
A worn or fouled spark plug causes inconsistent ignition. If your mower starts briefly then dies, the spark may be too weak to sustain combustion.
Fix:
- Remove and inspect the plug for carbon or oil buildup.
- Clean or replace it if it’s corroded or worn.
- Ensure the plug gap is set correctly (consult your owner’s manual).
6. Clogged Fuel Cap Vent
Most gas mower caps have a small vent hole to equalize pressure in the tank. If this vent is clogged, fuel flow stops after a few seconds.
Fix:
- Remove the gas cap and start the mower.
- If it stays running, clean or replace the cap.
7. Idle Speed Set Too Low
If your mower starts but dies at idle, the idle adjustment screw on the carburetor may be set too low.
Fix:
- Locate the idle screw and slowly turn it clockwise until the engine maintains a steady idle.
8. Moisture in the Fuel System
Water in the fuel can prevent proper combustion. This often happens after rain or if the mower was stored in a damp area.
Fix:
- Drain fuel, dry the tank, and refill with fresh gasoline.
- Add a fuel additive like Heet to absorb moisture.
9. Clogged or Damaged Exhaust/Muffler
A blocked muffler or spark arrestor screen restricts airflow and causes stalling.
Fix:
- Clean out carbon buildup or replace the spark arrestor if necessary.
10. Faulty Safety Switch
Modern mowers include safety switches (seat, blade, handle, or brake lever). If any are faulty, the mower will shut off automatically.
Fix:
- Test each safety switch with a multimeter.
- Replace any defective ones.
🛠️ Brand-Specific Fixes
Each brand has slightly different designs, so let’s break down brand-based troubleshooting for this problem.
1. Honda Lawn Mower Starts Then Dies
Honda mowers are reliable but often face carburetor and fuel issues due to their sensitive engine tuning.
Common Fixes:
- Clean the carburetor thoroughly.
- Replace the fuel filter and use fresh fuel.
- Check the auto-choke system for proper function.
- Replace spark plug (NGK BPR5ES is common).
Pro Tip:
Use Honda’s OEM carburetor cleaner and avoid aftermarket carb kits—they often don’t fit well.
2. Craftsman Mower Starts but Won’t Stay Running
Craftsman mowers (especially with Briggs & Stratton engines) often stall due to a dirty carb jet or old gas.
Fixes:
- Remove the carburetor bowl and clean the main jet with a thin wire.
- Replace the air filter if clogged with grass dust.
- Clean the vent hole in the fuel cap.
Extra Tip:
If it runs only with choke on, the carb jet is definitely blocked.
3. Toro Lawn Mower Starts Then Stalls
Toro’s self-propelled mowers often face fuel line or carb issues.
Fixes:
- Replace the fuel line if cracked.
- Drain fuel and add fresh gas with stabilizer.
- Adjust the idle screw slightly to raise idle speed.
Maintenance Tip:
Toro recommends changing oil and filter every 25 hours of use — dirty oil can also affect smooth operation.
4. Husqvarna Lawn Mower Starts Then Dies
Husqvarna mowers with Kohler or Briggs engines may stall due to ignition or carburetion issues.
Fixes:
- Clean or replace the spark plug (look for fouling).
- Check the ignition coil if spark is weak.
- Inspect air intake and filter box for clogging.
Pro Tip:
Husqvarna mowers stored in damp garages may have moisture in the carb bowl — dry it thoroughly.
5. Troy-Bilt Mower Starts Then Dies
Troy-Bilt push mowers commonly stall from fuel contamination or a clogged bowl nut jet.
Fixes:
- Clean the carburetor bowl and jet.
- Replace the fuel filter.
- Drain stale gas and use ethanol-free fuel.
Tip:
Add SeaFoam Motor Treatment to keep Troy-Bilt engines clean and running smoothly.
6. John Deere Lawn Mower Starts Then Dies
For John Deere riding mowers, electrical or fuel delivery problems are common.
Fixes:
- Check the seat safety switch and fuel solenoid.
- Clean the carburetor and fuel filter.
- Make sure the choke cable is not stuck.
- Inspect the fuel pump for debris or weak flow.
Tip:
Use John Deere’s branded fuel stabilizer during winter storage.
🧰 Step-by-Step Troubleshooting Checklist
Follow these steps in order for any mower brand:
| Step | What to Check | Action |
|---|---|---|
| 1 | Fuel Quality | Drain and replace with fresh gas |
| 2 | Air Filter | Clean or replace |
| 3 | Spark Plug | Clean or replace, check gap |
| 4 | Carburetor | Clean with carb cleaner or rebuild |
| 5 | Fuel Cap Vent | Clean vent hole |
| 6 | Fuel Filter | Replace if dirty |
| 7 | Idle Speed | Adjust screw slightly |
| 8 | Safety Switches | Test and replace faulty ones |
| 9 | Exhaust | Clean muffler/spark arrestor |
| 10 | Electrical (if applicable) | Check battery and solenoid on riding mowers |
⚙️ Preventive Maintenance Tips
- Use fresh, ethanol-free gasoline whenever possible.
- Run the mower dry before winter storage to prevent carb issues.
- Replace air and fuel filters annually.
- Clean or replace spark plugs each season.
- Add a fuel stabilizer to every new tank.
- Store in a dry, covered area to prevent moisture buildup.
🧩 When to Seek Professional Help
If you’ve cleaned the carburetor, replaced filters, and checked fuel and spark—but your mower still stalls—there could be deeper issues like:
- A failing ignition coil,
- Bad governor spring,
- Compression loss,
- Electrical faults (for battery or electric models).
A small-engine technician can diagnose these using specialized tools.
❓ Frequently Asked Questions (FAQs)
1. Why does my lawn mower start and then immediately die?
Usually due to a dirty carburetor or old fuel restricting flow. Cleaning the carb and refueling solves it in most cases.
2. My mower runs only on choke—what does that mean?
That means your carburetor’s main jet is partially blocked, restricting fuel flow.
3. Can a bad spark plug cause stalling?
Yes. A fouled or damaged spark plug causes misfires or weak combustion, leading to stalling.
4. Why does my electric mower start and stop right away?
This could be a safety interlock issue, a faulty battery connection, or overheating motor protection engaging.
5. How often should I clean my mower’s carburetor?
At least once per season, or whenever your mower starts surging, stalling, or idling rough.
6. Should I use fuel stabilizer in every tank?
Yes, especially if you use ethanol-blended gasoline. It keeps the fuel system clean and prevents varnish buildup.
7. Why does my mower stall when I engage the blades?
That’s often due to a weak engine, clogged deck, or a safety switch cutting off the engine. Check the blade engagement cable too.
✅ Final Thoughts
A lawn mower that starts but won’t stay running is a nuisance, but the fix is often simple—cleaning, replacing a few parts, or adjusting idle speed can make your mower run like new.
Whether you own a Honda, Craftsman, Toro, Husqvarna, John Deere, or Troy-Bilt, the same fundamentals apply:
- Clean fuel,
- Proper airflow,
- Strong spark,
- Regular maintenance.
By following the steps above, you can save time, money, and frustration—and get back to mowing without interruptions.
I’m David man behind Lawn Mowerly; I’ve been dealing with lawnmowers and Tractors with my father since I was a kid. I know every make and model and what each one is capable of and love helping people find the perfect equipment for their needs.