Is your lawn mower sputtering, surging, bogging down, or just running rough? You’re not alone. A mower that starts but doesn’t run smoothly can make mowing frustrating, leave your yard uneven, and even risk long-term engine damage if ignored. The good news? Most “not running right” problems have simple causes and easy fixes. Here’s a step-by-step guide to help you troubleshoot and repair your rough-running lawn mower.
Quick Picks: Common Reasons a Lawn Mower Runs Poorly
- Dirty Air Filter: Chokes the engine, causing surging or stalling.
- Old or Bad Gasoline: Stale fuel causes sputtering, surging, and power loss.
- Dirty or Clogged Carburetor: Restricts fuel flow, leading to rough running or hunting at idle.
- Fouled Spark Plug: Weak or erratic spark results in misfires and uneven operation.
- Blocked or Dirty Fuel Filter: Not enough fuel reaches the engine.
- Water in the Fuel: Causes hesitation, surging, or rough idle.
- Vacuum Leaks: Cracked primer hoses or gaskets let in unmetered air, making the engine surge or hunt.
- Dull or Damaged Blade: Overloads the engine, causing it to bog down, especially in thick grass.
- Throttle or Governor Linkage Issues: If these parts stick or are misadjusted, the engine can surge or rev inconsistently.
Buyer’s Guide: Tools & Supplies for Quick Fixes
- Socket set & screwdrivers: For plug, filter, and carburetor access.
- Carburetor cleaner spray: To clean jets and passages.
- New air filter and spark plug: Always use the correct type for your mower.
- Replacement fuel filter and fresh gasoline: For restoring clean fuel flow.
- Work gloves and rags: For safety and cleanup.
- Owner’s manual: For diagrams and specifications.
Step-by-Step: How to Fix a Lawn Mower That’s Not Running Right
1. Replace or Clean the Air Filter
- Remove the air filter cover. If the filter is dirty or oily, replace it or clean (foam types can be washed).
- A clean air filter restores proper airflow and improves running immediately.
2. Drain Old Gas and Add Fresh Fuel
- Empty any gas left from last season—old fuel causes rough running.
- Refill with fresh, high-quality gasoline (use stabilizer if storing fuel for more than a month).
3. Clean the Carburetor
- Remove the air filter and spray carburetor cleaner into the carb intake.
- For persistent issues, remove and clean the carburetor thoroughly, paying close attention to jets and passages.
4. Check and Replace the Spark Plug
- Remove the spark plug and inspect for black, oily, or corroded electrodes.
- Clean with a wire brush or replace for reliable spark and smoother running.
5. Replace the Fuel Filter and Inspect Lines
- Locate the in-line fuel filter and replace if dirty or discolored.
- Check for cracks, kinks, or leaks in the fuel lines.
6. Check for Water in the Fuel
- Look for water at the bottom of the tank or in the carb bowl (it looks separate from gas).
- Drain and refill with fresh fuel if water is present.
7. Inspect Throttle, Governor, and Blade
- Ensure all linkages move freely and return to position when released.
- Sharpen or replace a dull blade—this makes mowing smoother and puts less strain on the engine.
Comparison Table: Lawn Mower Running Problems & Solutions
| Problem | Solution | Difficulty | Parts Needed |
|---|---|---|---|
| Dirty Air Filter | Clean or replace filter | Easy | Air filter |
| Old/Bad Gas | Drain and refill with fresh gas | Easy | Gasoline |
| Dirty Carburetor | Clean/rebuild carburetor | Easy-Medium | Carb cleaner |
| Fouled Spark Plug | Clean or replace plug | Easy | Spark plug |
| Blocked Fuel Filter/Line | Replace filter/line | Easy | Fuel filter/line |
| Water in Fuel | Drain tank and refill | Easy | Gasoline |
| Vacuum Leak | Replace hose/gasket | Easy | Primer hose/gasket |
| Dull/Damaged Blade | Sharpen or replace blade | Easy | Blade |
| Throttle/Governor Issues | Adjust/repair linkage | Easy-Medium | Springs, manual |
Frequently Asked Questions
Why is my mower surging or hunting at idle?
This usually means a dirty carburetor, clogged jet, vacuum leak, or blocked fuel line. Cleaning and tightening connections usually solves it.
Can bad gas really cause my mower to run rough?
Absolutely—stale or ethanol-blended fuel breaks down fast and causes running problems. Always use fresh gas for best performance.
What if my mower only runs with the choke on?
This points to a clogged carburetor or vacuum leak—there’s not enough fuel being delivered unless the mixture is artificially enriched.
How often should I change filters and plugs?
At least once per mowing season, or more often in dusty or heavy-use conditions.
When should I call a professional?
If you’ve checked all the basics and your mower still runs poorly, you may have deeper engine or electrical problems—time for a small engine technician.
Conclusion
If your lawn mower isn’t running right, check the basics first—fresh gas, clean air filter, new spark plug, and a clean carburetor solve most problems. With simple maintenance and a few easy fixes, your mower will be running strong, giving you a clean, even cut all season long!