There’s nothing more frustrating than firing up your lawn mower, only to have it stall after a few seconds or minutes. If your mower starts but won’t stay on, you’re not alone—this is one of the most common problems for both push and riding mowers. The good news? Most causes are easy to identify and repair at home. Here’s your complete guide to fixing a lawn mower that won’t keep running, including the top causes, step-by-step solutions, and maintenance tips for a healthy, reliable engine.
Quick Picks: Why Your Lawn Mower Won’t Stay On
- Clogged Carburetor: Old or bad fuel gums up the jets, starving the engine after the first few seconds.
- Dirty Air Filter: Blocks air, causing the engine to stall out.
- Bad or Old Gasoline: Fuel that’s stale or has water in it fails to burn, causing sputtering and shut-offs.
- Faulty Spark Plug: Weak spark leads to stalling after startup.
- Blocked Fuel Line or Filter: Limits fuel flow, so the engine dies once the bowl empties.
- Choke or Throttle Issues: Stuck choke floods the engine or won’t allow enough air in after starting.
- Vacuum or Gasket Leaks: Rare, but a leaking gasket or intake can upset the fuel/air mix.
Buyer’s Guide: Tools & Supplies for Fast Fixes
- Socket wrench set: For spark plug and carburetor removal.
- Carburetor cleaner spray: Essential for cleaning out fuel residue.
- Replacement air filter: For better airflow and engine life.
- New spark plug: Always use the correct type for your mower.
- Fuel line and filter: For replacing blocked or damaged components.
- Fresh gasoline: Never use old or separated fuel.
- Work gloves & eye protection: For safety during repairs.
Step-by-Step Guide: How to Fix a Lawn Mower That Won’t Stay On
1. Replace Old or Bad Gasoline
- Drain all the old fuel from the tank (use a siphon or carefully tilt the mower).
- Refill with fresh, clean gas—avoid using fuel older than 30 days.
- If possible, add a stabilizer to new fuel for better storage life.
2. Clean or Replace the Air Filter
- Remove the air filter cover and take out the filter.
- If it’s dirty or clogged, replace it (or wash and dry if foam style).
- A clean filter restores proper airflow, helping the engine stay running.
3. Clean the Carburetor
- Remove the air filter and spray carburetor cleaner directly into the intake or bowl.
- Let it sit for 5–10 minutes, then try to start the engine.
- If the engine runs then stalls again, you may need to remove and deep-clean the carburetor (especially if fuel was left in the mower over winter).
- If you’re not comfortable disassembling, most shops can clean or rebuild a carburetor quickly and affordably.
4. Check and Replace the Spark Plug
- Remove the spark plug with a socket wrench.
- Look for black carbon, oil, or signs of wear—clean or replace the plug as needed.
- Make sure the spark plug wire is securely attached after reinstalling.
5. Inspect and Replace the Fuel Filter & Line
- Locate the fuel filter (usually in the line between the tank and carburetor).
- If it looks dirty or fuel flow is restricted, replace it.
- Check the fuel line for cracks, clogs, or pinches and replace as needed.
6. Adjust Choke and Throttle Linkages
- Make sure the choke closes for cold starts and opens fully as the engine warms up.
- Check throttle cable and linkages for binding, stiffness, or misadjustment.
- Lubricate or adjust as needed for smooth movement.
7. Look for Gasket or Vacuum Leaks
- Inspect carburetor and intake gaskets for cracks, gaps, or air leaks.
- Spray carburetor cleaner around the base while the engine runs—if the RPM changes, you likely have a leak to fix.
- Replace gaskets as needed to ensure a tight seal.
Comparison Table: Why Mowers Stall After Starting
| Problem | Solution | Difficulty | Parts Needed |
|---|---|---|---|
| Old/Bad Gas | Drain and refill with fresh fuel | Easy | Gasoline |
| Clogged Carburetor | Spray or deep clean carb | Easy-Medium | Carb cleaner |
| Dirty Air Filter | Replace or clean filter | Easy | Air filter |
| Bad Spark Plug | Clean or replace plug | Easy | Spark plug |
| Blocked Fuel Line/Filter | Replace line/filter | Easy | Fuel filter/line |
| Choke/Throttle Issue | Adjust or repair linkage | Easy | Tools, manual |
| Vacuum/Gasket Leak | Replace gasket, fix leak | Medium | Gasket, tools |
Frequently Asked Questions
Why does my mower start and then die after a few seconds?
This usually means a clogged carburetor, bad gas, or blocked air filter. The engine burns what little fuel is left in the carb, then stalls out.
Can a bad spark plug cause my mower to stall?
Yes. A fouled or failing plug may work briefly but fail under load, causing the mower to shut off soon after starting.
How often should I change the air filter and spark plug?
Replace both at least once per mowing season, or more often if you mow dusty or dirty areas.
Is it okay to use starting fluid?
Only for brief troubleshooting—don’t rely on starting fluid long-term, or you may mask deeper issues like a clogged carb or old fuel.
What if none of these fixes work?
If you’ve tried every step and your mower still won’t stay on, you may have a more serious internal engine or electrical problem. Consider professional service at that point.
Conclusion
If your lawn mower won’t keep running, most fixes are quick and affordable: clean the carburetor, change the air filter and spark plug, and always use fresh gas. With these steps and regular maintenance, your mower will be reliable, powerful, and ready for every mowing season!