Lawnmower engines, like other engines, need just three things to run: air, fuel, and spark. When your mower refuses to fire up, 9/10 times it is because one of these essentials is missing or compromised. The key to getting it fixed soon is knowing where to look first.
Historic data shows that 85% of starting problems cost under $50 to fix and can be resolved in less than an hour with just basic tools..
Here are 5 common reasons for your lawnmower not starting.
Reason #1: Fuel is Old or Contaminated
If your lawnmower won't start after sitting all winter, it's usually because of old or contaminated fuel. Lawnmower starting problems related to old fuel account for around 40% of complaints. Gasoline begins breaking down after just 30 days, and ethanol fuel absorbs moisture that creates these starting headaches.
What causes fuel issues?
Ethanol-blended gasoline separates over time, leaving deposits that clog carburetor jets and fuel lines. Water contamination causes poor combustion and prevents proper ignition.
Cost to fix: $15-20 for fresh fuel, $10 for an oil siphon pump $10 if needed
How to Fix Old Contaminated Fuel
- Drain the fuel tank completely using a siphon pump
- Check if the oil smells like gasoline - if so, change the oil too
- Refill with fresh fuel that is less than 30 days old
- Add a fuel stabilizer if you plan to store the mower for periods over 30 days
Reason #2: The Spark Plug Is Dirty Spark
Spark plug problems cause about 25% of lawnmower starting issues and are often the easiest fix. A dirty plug can't create the spark needed to ignite fuel in the engine, leading to startup issues. These are designed to typically last around 100 operating hours, but can fail sooner if your mower engine runs rich or oil contaminates the combustion chamber.
- What causes spark plug failures: Carbon buildup from rich fuel mixtures, or simply normal wear from use.
- Cost to fix: $5-15 for a spark plug replacement
How to Fix a Dirty Spark Plug
- Remove the spark plug wire and unscrew it with a socket wrench
- Inspect the electrode for carbon buildup, oil, or worn electrodes
- Clean with brake cleaner and a wire brush, or replace if worn
- Gap new plugs to manufacturer specification (usually 0.030")
- Tighten to the proper torque
Reason #3: Air Filter is Clogged
Clogged air filters account for roughly 20% of mower starting problems and often cause poor performance before complete failure. A dirty air filter messes with the air/fuel mixture, making starting difficult or impossible. Paper filters should be replaced every season or 25 operating hours, while foam filters need cleaning every 10 hours.
What happens with clogged filters: Restricted airflow creates an overly rich fuel mixture that won't ignite properly, so the engine may turn over, but won't catch and run.
Cost to fix: $8-20 for a replacement air filter
How to Clean a Lawnmower Clogged Air Filter
- Remove the air filter cover
- Inspect the filter condition. For foam filters, wash in warm soapy water, then rinse and dry completely
- Apply a light coating of engine oil to the cleaned foam filter before re-installing
Reason #4: Carburetor Problems
Carburator issues are behind around 10% of starting failures, but can be the most expensive to fix properly. The carburetor mixes fuel and air for combustion, and when it gets dirty or clogged, your mower will struggle to start.
- What causes carburetor problems: Dirty fuel, old gasoline deposits, and debris blocking jets and passages. Stuck float valves can also flood the engine or prevent fuel flow entirely.
- Cost to fix: $15 for carburetor cleaner $15, $75-120 for a professional cleaning
How To Fix Carburetor Problems
- Remove the air filter to access the carburetor throat
- Spray carburetor cleaner into the throat while the engine is off
- Tap the sides of the carburetor gently to help dislodge debris
- For persistent problems, remove the carburetor bowl and clean the jets
- Professional cleaning is recommended for complex carburetor issues
Craftsman vs Honda vs Toro: Most likely reasons for not starting
| Brand | Most Common Issue | Main Cause | Average Repair Cost |
| Craftsman | Carburetor problems | Cheap fuel system components | $75-120 |
| Honda | Bad spark plug | Tight engine tolerances | $10-15 |
| Toro | Air filter clogging | High-performance air intake | $15-25 |
When is it time to get a new Lawn Mower?
Sometimes a lawnmower that won't start indicates problems that aren't worth fixing financially. A few such instances include:
- A seized engine from a lack of oil, where the repair costs exceed 60% of the mower’s value
- Multiple simultaneous failures of main components
- Professional diagnosis reveals internal engine damage
Buy Top Quality Lawn Mowers from AHM Corps
Instead of wondering “why won't my lawnmower start” every weekend, switch to AHM's hybrid lawnmowers that eliminate many common starting issues through intelligent design.
1. AHM LM-55 Hybrid Remote Control Mower - $3,399.99
The LM-55 hybrid lawnmower is powered by a rechargeable battery and a 5 hp 4-stroke engine; it easily tackles slopes up to 45° and covers up to 0.25 acres with no sweat. Adjust the cutting height from 0.4" to 5" at the push of a button using the remote control.
- 5 HP 4-stroke engine designed to start reliably each time with proper fuel management
- 12V battery backup that eliminates starting issues
- Remote operation prevents engine flooding from user error
2. AHM X80 Remote Control Mower - $3,799.99
The X80 remote control mower is the perfect choice for larger properties that require maximum reliability. With a 3280 ft. remote range and dual controls—remote and joystick—mowing is easier than ever. The hybrid engine combines a 13.6 hp gas engine and dual 650W motors for 1034 lbf of power, cutting fuel use while tackling up to 5 acres.
Key features:
- 31.5-inch cutting width with a reliable 13.6 HP hybrid power system
- Intelligent fuel management that prevents carburetor contamination
- Professional-grade components that reduce maintenance-related starting issues
Conclusion
When trying to fix a lawnmower that won’t start, make sure to start with the basics - fresh fuel, a clean spark plug, and a new air filter. These three items will solve most starting problems and cost less than $40 total.
Only move to more complex carburetor work if the basic maintenance doesn't resolve the issue. Once you start understanding these starting failure patterns, expensive repair shop visits will become a thing of the past.
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