If your lawn mower fires up but stalls after a few seconds or minutes, you’re not alone. This is a classic mower problem that can quickly ruin your weekend plans and leave your grass overgrown. Fortunately, a mower that won’t stay running is usually caused by a handful of simple, fixable issues. This guide covers every common cause, easy solutions, and maintenance tips to keep your mower running strong all season.
Quick Picks: Top Reasons a Lawn Mower Won’t Stay Running
- Clogged Carburetor: Old fuel gums up the carburetor, blocking jets and starving the engine.
- Dirty or Clogged Air Filter: Not enough air reaches the engine, causing it to stall out.
- Bad or Stale Gasoline: Old fuel won’t combust well and can quickly kill the engine after it starts.
- Fouled or Damaged Spark Plug: Weak or inconsistent spark won’t keep the engine firing.
- Blocked Fuel Filter or Fuel Line: Debris prevents steady fuel flow, so the engine dies after burning what’s in the bowl.
- Choke or Throttle Linkage Problems: If the choke doesn’t open or the throttle sticks, your mower can stall as it warms up.
- Vacuum Leak or Bad Gasket: Rare, but a leaking intake gasket can upset the fuel/air mix and cause stalling.
Buyer’s Guide: Tools & Supplies You’ll Need
- Carburetor cleaner spray: For dissolving gunk in the carburetor.
- Replacement air filter: Get the correct size for your model.
- New spark plug: Always use the recommended type and gap for your mower.
- Fuel line and fuel filter: For replacing clogged or cracked components.
- Fresh gasoline: Never use last season’s fuel.
- Socket wrench set & screwdriver: For plug and carburetor removal.
- Work gloves & eye protection: Safety first when working with engines and fuel.
Step-by-Step Guide: How to Fix a Lawn Mower That Won’t Stay Running
1. Drain Old Gas and Use Fresh Fuel
- Siphon or pour out all old fuel from the tank (tilt the mower carefully with the air filter up).
- Refill with fresh gasoline—preferably less than 30 days old. Use fuel stabilizer if you mow infrequently.
2. Clean or Replace the Air Filter
- Remove the air filter cover and check the filter for dirt, debris, or oil.
- Replace if dirty or wet; clean if it’s foam and washable. A clean filter means better airflow and steady running.
3. Clean the Carburetor
- Remove the air filter and spray carburetor cleaner into the carb intake.
- Let sit for 5–10 minutes, then try starting the engine.
- If the engine starts and stalls again, remove and deep-clean the carburetor (or have it serviced).
4. Check and Replace the Spark Plug
- Remove the spark plug with a socket wrench and inspect for black carbon, oil, or damage.
- Clean or replace with a new, properly gapped plug.
- Reattach the wire securely before testing the mower again.
5. Inspect and Replace the Fuel Filter & Fuel Line
- Trace the fuel line from tank to carburetor. Look for kinks, cracks, or blockages.
- Replace the fuel filter if it’s dirty or flow is restricted. Make sure lines are clear and leak-free.
6. Check Choke and Throttle Operation
- Ensure the choke closes fully when starting cold and opens as the engine warms up.
- Make sure throttle and choke linkages move smoothly—lubricate or adjust if needed.
7. Look for Gasket or Vacuum Leaks
- Inspect around the carburetor and intake for signs of leaking or damaged gaskets.
- Spray carburetor cleaner at the base while the engine runs—if idle speed changes, you have a leak that needs a new gasket.
Comparison Table: Why Mowers Won’t Stay Running
| Problem | Solution | Difficulty | Parts Needed |
|---|---|---|---|
| Clogged Carburetor | Clean with spray or rebuild | Easy-Medium | Carb cleaner, gaskets |
| Dirty Air Filter | Replace or clean filter | Easy | Air filter |
| Old/Bad Gas | Drain and refill tank | Easy | Fresh gasoline |
| Bad Spark Plug | Replace spark plug | Easy | Spark plug |
| Blocked Fuel Filter/Line | Replace filter or line | Easy | Fuel filter/line |
| Choke/Throttle Linkage Issue | Adjust or lubricate linkage | Easy | Lubricant, tools |
| Gasket/Vacuum Leak | Replace gasket, seal leak | Medium | Gasket |
Frequently Asked Questions
Why does my mower start and then die quickly?
This almost always means a fuel flow problem—clogged carburetor, bad gas, or a blocked filter. The engine burns what little fuel it gets, then shuts down.
How often should I replace my air filter and spark plug?
Once a season is best, or more often if you mow in dusty, dirty conditions or use your mower heavily.
Can a bad carburetor gasket cause stalling?
Yes. A leaking gasket lets air in, making the mixture too lean, which causes the engine to stall.
Do I need to use fuel stabilizer?
It’s a great idea if you mow infrequently or store fuel over winter. Stabilizer keeps gas from breaking down and gumming up the carburetor.
What if my mower won’t stay running after all these steps?
If you’ve tried every basic fix and it still stalls, the problem could be a more serious engine or electrical issue. Time to consult a professional for a full diagnosis.
Conclusion
A mower that won’t stay running is almost always fixable with some routine maintenance and the right checks. Fresh fuel, a clean filter, and a working carburetor will keep your mower starting easily and running strong—so you can spend less time fixing and more time enjoying a beautiful, well-cut lawn!