To fix a lawn mower that won’t start, work through fuel, air, spark, and safety switches in order, then clean the carburetor if needed.
Stuck pull cord. Silence from an electric start. A cough and stall. Different symptoms point to the same core loop: the engine needs fresh fuel, free air, strong spark, and the safety system set. The fix is a checklist you can run in minutes, with a few deeper steps if the basics fail.
Fast Checklist: Symptoms And Likely Fixes
Use this table as your first scan. Match what your mower does to the closest row, then follow the quick check before moving down the list.
| Symptom | Likely Cause | Quick Check / Fix |
|---|---|---|
| No sound, pull feels normal | No fuel, safety bar not engaged | Add fresh gas; hold the bail bar tight; retry |
| Engine fires then dies | Stale fuel, clogged jet, blocked cap vent | Drain tank; refill; crack fuel cap briefly; clean carb |
| Pull cord is stiff | Blade jam, brake engaged | Unplug plug; tip back; clear debris; squeeze bail |
| Repeated clicking on key start | Weak battery or corroded cables | Charge battery; clean posts; check ground |
| Backfire or sputter | Old plug, wrong choke | Set choke for cold; replace plug |
| Flooded smell, wet plug | Over-choke, stuck float | Dry plug; full throttle, no choke; pull a few times |
| Nothing unless seat is weighted | Interlock switch working | Stay seated or bypass only for diagnosis; do not run bypassed |
| Runs rough under load | Clogged air filter, dull blade | Swap filter; sharpen blade |
Safety First: Quick Setup Before You Start
Pull the spark plug wire before touching the blade. Wear gloves and eye protection. Work outdoors. If you tip a walk-behind, tip the handle down and carb side up so oil stays out of the air filter.
How To Repair A Lawn Mower That Won’t Start: Step-By-Step
Step 1: Confirm The Basics
Set the bail bar against the handle. On riders, set the brake and neutral. Check deck engagement is off. Add fuel to at least one third of the tank. Many mowers hate near-empty tanks on slopes.
Step 2: Rule Out Old Gas
Gasoline ages. Oxidation and gum form deposits that block fine passages. If fuel is older than a month or smells sour, drain it from the tank and bowl. Refill with fresh, name-brand regular, up to 10% ethanol if your manual allows. Add stabilizer if the can will sit.
Step 3: Give The Engine Clean Air
Pop the air filter cover. If the paper element is gray or caked, swap it. Foam pre-filters can be washed and dried. A starved engine may start only with the choke, then stall as soon as the choke opens.
Step 4: Check Spark In Two Minutes
Pull the plug boot, remove the plug, and look for fouling. Gap to spec from your manual. Clip the boot back on the plug, ground the threads to bare metal, and pull the cord. You should see a crisp blue snap. If it is weak or absent, install a new plug of the right heat range.
Step 5: Clear The Carburetor
Small jets clog easily. Close the fuel valve or pinch the line. Remove the bowl nut; that nut is often the main jet. Poke the tiny holes with a carb-safe wire and spray cleaner through each passage. Reassemble with a fresh gasket if the old one is brittle.
Step 6: Check The Fuel Path
Trace from tank to carb. Make sure the cap vent breathes. Look for a paper fuel filter; if dark, replace it. Squeeze the primer bulb, if fitted. On riders, follow hoses to the pump and filter and replace suspect parts.
Step 7: Inspect Safety Interlocks
Walk-behinds use a cable that pulls the brake and kills the ignition when released. If the lever feels loose, tighten the adjuster at the handle. Riders use seat, brake, and blade switches in a series. A failed switch can block spark or starter power. Test one at a time and replace the bad one.
Step 8: Battery, Starter, And Cables (Riders)
If the starter clicks, measure battery voltage at rest and while cranking. Clean corrosion from posts and grounds. Check the solenoid. Replace a swollen or low-reading battery. Make sure the ground strap to the frame is tight.
Why These Steps Work
A mower is simple. Fuel plus air flows in, the spark lights it, and rotating mass keeps the cycle going. Stale fuel blocks jets. A plugged filter chokes air. A worn plug misfires. Interlocks stop spark or starter when controls aren’t set. Solving the start is matching symptom to part of that loop.
Pro Tips For A First-Pull Start Next Time
Use Fresh Fuel And Stabilizer
Buy gas in small amounts during the mowing season. Add stabilizer to the can if it will sit. Many makers approve up to E10; avoid higher blends unless your manual says so.
Keep Filters And Plugs On A Schedule
Swap the air filter yearly on dusty lawns. Replace the spark plug every season or 100 hours. Keep a spare plug and pull rope on the shelf so a rough Saturday doesn’t end early.
Clean The Deck And Blade
Grass packed under the deck loads the engine at startup. Scrape the deck clean. Sharpen the blade; a dull edge drags and hides other problems.
Store It Right
At season end, run the carb dry or store with treated fuel. Park on level ground. Cover the machine and the gas can to reduce moisture swings.
For deeper background, see Briggs & Stratton fuel storage and the official Honda fuel recommendations.
Electric And Battery Mowers: Quick Notes
Verify the safety bail is pulled in. For corded units, try a different outlet and check GFCI. For battery mowers, seat the pack until it clicks, try a spare pack, and check pack LEDs. Clean grass from the blade area so the motor can spin up without a heavy load.
When The Carb Still Won’t Behave
If the engine only runs on choke or surges, the pilot jet is likely dirty. Remove the carb, soak the body in cleaner, and blow passages with compressed air. Replace the bowl gasket, float needle, and seat. On many Honda-style carbs, the tiny pilot jet is hidden under a rubber plug.
Starter Fluid: Use With Care
A brief shot into the intake can confirm spark only. Do not spray into a hot muffler. If it fires on spray then stalls, you still have a fuel path issue to solve.
Check Compression If All Else Fails
Hold the bail, open the throttle, and pull a few times with a gauge in place. Readings below factory spec hint at worn rings, a sheared flywheel key, or a valve issue. At that point, a shop visit makes sense.
Maintenance Intervals And Payoff
Routine care keeps starts easy and repairs rare. Use this schedule as a baseline, then adjust for dusty yards or heavy growth.
| Task | Interval | Why It Helps |
|---|---|---|
| Change engine oil | Annually or 50 hours | Fresh oil improves sealing and starting |
| Replace air filter | Annually | Restores airflow and idle quality |
| Replace spark plug | Annually | Sharp spark lights cold mixes |
| Drain or treat fuel | Season end | Prevents gum that clogs jets |
| Sharpen blade | Every 25 hours | Reduces startup load |
| Inspect cables/switches | Mid-season | Catches interlock faults early |
Troubleshooting By Symptom
Pull Cord Won’t Move
Disconnect the plug wire. Tip the mower back and pry out sticks or packed clumps. If the blade spins free, pull the cord again. A broken recoil spring or jammed pawls calls for a recoil service kit.
Starts, Then Stalls While Mowing
Pop the gas cap and see if it recovers; a blocked vent builds vacuum and starves fuel flow. Swap the fuel filter. Clean the carb’s main and pilot jets. Check for water beads in the bowl.
Cranks, No Fire (Rider)
Seat switch, brake switch, or PTO switch can block spark or starter feed. Sit firmly, set brake, and cycle the PTO switch a few times. If spark is present, test fuel delivery and compression next.
Backfire On Shutoff
Let the engine idle for a few seconds before turning the key off. Raw fuel can ignite in the hot muffler if shut down from high throttle.
What To Buy For Your Kit
Keep a tune-up set on hand: one spark plug that matches your engine code, air filter, fuel filter, carb bowl gasket, pull rope, carb cleaner, and dielectric grease for battery posts. Label your gas can and treat it the day you fill it.
Common Mistakes That Waste Time
- Skipping the bail bar. Many walk-behinds need the bar squeezed before spark arrives, even while you pull the cord.
- Over-choking a warm engine. Use half or no choke once the block has heat, or you will flood the plug fast.
- Letting the tank run low. Slopes and bumps uncover the pickup and starve the carb; fill to one third or more.
- Using last year’s gas. Old fuel causes hard starts and sticky jets; buy small amounts and treat the can.
- Forgetting the blade control. On riders, the PTO switch must be off and the brake set or the starter feed stays blocked.
- Cranking forever. Ten short pulls beat one long pull; give the cylinder a breather to clear rich mix between pulls.
When To Visit A Shop
Shops have ultrasonic cleaners, leak-down testers, and OEM parts. If a mower still won’t start after fresh fuel, a new plug, a clean filter, and a carb clean, book service. Bring the model and engine codes and describe the exact symptom so the tech can jump to the right test.