A gas lawn mower that won’t start usually needs fresh fuel, clear air, strong spark, and correct controls—run these steps to bring it back.
You’re ready to cut, pull the cord, and get nothing. No worries. This guide gives fast checks first, then deeper fixes. Follow along in order; most no-start issues resolve without a shop visit. For step-by-step videos from an engine maker, see Briggs & Stratton’s mower starting guide. Handle gasoline with care and work outdoors safely in daylight.
Quick Wins Before Tools Come Out
- Check the fuel shutoff valve if your mower has one; set to ON.
- Hold the safety bar tight to the handle while pulling the starter.
- Set the choke or primer for a cold start; open the choke once it fires.
- Verify the blade control is disengaged on combo drive/blade systems.
- Try starting on a firm surface so the blade can spin freely.
Fast Diagnosis Table
| Symptom | Likely Cause | What To Do |
|---|---|---|
| No sound at all | Safety bar not held, bad switch, dead battery on electric-start | Squeeze the bar, inspect the bail cable, charge the battery |
| Cord pulls, no fire | Old gas, wrong fuel, flooded engine | Replace fuel, set choke correctly, open throttle and try again |
| Starts then dies | Clogged jet, blocked vent, dirty filter | Clean or replace air filter, crack the gas cap, clean carburetor |
| Hard start when warm | Sticking choke or needle, vapor lock | Open choke, let it cool a minute, check linkage |
| Cord stuck | Blade jam, hydro-lock from tipped mower | Remove spark plug, clear debris, pull cord to expel fuel |
| Backfire or pops | Loose spark plug or wrong gap | Tighten plug, set gap, replace if worn |
Gas Mower Not Starting: First Five Checks
1) Fuel age and type
Small engines are picky about fuel. Use fresh gasoline, ideally less than 30 days old. Avoid blends over E10; E15 or higher can trigger hard starts and damage. If the gas smells sour or looks dark, drain the tank and carburetor bowl, then refill. A stabilizer helps during the season; it slows oxidation and moisture uptake.
2) Safety controls and starting procedure
Most walk-behind mowers use a safety bar that must be held against the handle for spark. Some models add a key, a neutral/drive lever, or a blade clutch. Confirm the bar cable moves the engine brake arm fully. For cold starts: set the choke or press the primer per your manual. For warm restarts: open the choke and use half throttle.
3) Airflow: air filter and intake
A clogged filter chokes the engine. Pop the cover, tap out loose dust, and replace foam or paper elements that look saturated or torn. Inspect the intake tube for nests or grass packed behind the shroud. Clean the cooling fins while you’re there.
4) Spark: plug, lead, and coil
Pull the plug cap off and check that the boot grips firmly. Remove the plug with a wrench. If it’s sooty, oily, cracked, or the electrode is rounded, install a new one and set the gap to the spec on your engine sticker. Thread by hand, then snug. To quick-test spark, ground the plug body to metal and pull the cord; look for a sharp blue snap.
5) Carburetor and choke
If the mower only runs on full choke or stalls after priming, the main jet is likely gummed. Shut off fuel. Remove the bowl nut (often the jet), clean passages with carb cleaner and a fine wire, and reinstall with a new bowl gasket if needed. Make sure the choke plate opens once the engine lights.
Targeted Fixes By Symptom
Pull Cord Won’t Budge
Unplug the spark lead. Tip the mower spark-plug-side up. Clear packed grass, rope, or sticks under the deck. If the blade moves, the starter should pull again. If the cord is free with the plug out and a mist sprays from the hole, the cylinder is hydro-locked from being tipped wrong; pull the cord several times to clear, then refit the plug.
Starts, Runs A Few Seconds, Then Quits
Loosen the fuel cap. If it restarts, the cap vent is blocked and needs cleaning or replacement. If venting doesn’t help, the carburetor idle circuit may be dirty. Clean the bowl and jet, and replace the in-line fuel filter if fitted.
Only Starts On Choke, Lacks Power
This points to a restricted main jet or low float level. Clean the jet and emulsion tube. Confirm the float moves freely and the needle seats. Check the air filter too; a starved engine mimics a fuel fault.
Click At The Key, No Crank On Electric-Start
Charge the battery, then check the fuse, terminals, and ground strap. Look for corrosion at the solenoid and key switch. Verify the blade clutch or safety bar is in the start position; some mowers won’t crank unless the bail is pulled.
Loud Pop Through The Intake
Re-seat the spark plug and confirm the gap. Inspect the flywheel key if the mower hit a rock; a sheared key throws timing off. Replace the key and torque the blade and flywheel to spec.
Fuel, Air, Spark: What Each System Needs
Fuel System
Use the right gasoline and keep it fresh. Replace brittle fuel line and any cracked primer bulbs. If the tank has sediment, flush it into a clear container and wipe the pickup screen. Keep the tank vent clear so fuel flows.
Air System
An engine needs clean, steady airflow. Replace old filters, clear the snorkel, and remove rodent nests from shrouds. Good cooling keeps ignition parts healthy, too.
Ignition System
Spark depends on a sound plug, tight lead, correct coil gap, and a working stop switch. If spark is weak or absent, isolate the coil by disconnecting the kill wire; if spark returns, the switch or harness is shorted.
When A Gas Lawn Mower Won’t Start After Storage
Old fuel leaves varnish that glues needles, jets, and tiny check valves. Do this refresh:
- Drain the tank and carburetor bowl.
- Refill with fresh gas and a dose of stabilizer.
- Replace the spark plug and air filter if they’re tired.
- Clean the carburetor bowl and jet; replace the bowl gasket.
- Change oil on models with a separate oil sump.
Most mowers roar back after this cleanup.
Safe Fuel Handling
Work outside, away from flames. Cool the engine before opening the cap. Use a proper container with a tight spout. Wipe spills and let fumes clear before you pull the cord.
Second Diagnostics Table: Specs And Intervals
| Item | Typical Range | When To Service |
|---|---|---|
| Spark plug gap | 0.020–0.030 in (0.5–0.75 mm) | Inspect every season; replace yearly or 100 hours |
| Air filter | Foam or paper element | Check every 25 hours; replace when dirty or damaged |
| Oil (4-cycle) | SAE 10W-30 in many climates | Change after 5 hours on a new engine, then every 50 hours |
| Fuel | Unleaded up to E10, fresh | Replace if older than 30–60 days or after storage |
| Blade torque | Per manual (usually 35–60 ft-lb) | Check after blade service or impact |
| Battery (electric-start) | 12 V sealed | Charge monthly during off-season |
Prevent The Next No-Start
Build a quick routine:
- Buy small amounts of gas, or treat every can right away.
- Run the engine dry at season’s end, or shut the valve and drain the bowl.
- Swap the air filter and plug each spring.
- Keep the deck clean; packed grass traps heat near the coil.
- Log dates and hours on a strip of tape under the handle.
Simple Tool Kit You’ll Use Again
Keep these in a small bin:
- 13/16-inch or 5/8-inch spark plug socket and ratchet
- Flat and Phillips screwdrivers
- 10 mm and 13 mm wrenches
- Pliers and hose clamp pliers
- Carburetor cleaner and a set of jet wires
- Feeler gauge for setting plug and coil gaps
- Work gloves and safety glasses
FAQ-Style Notes You’ll Be Glad To Know
Can Tipping Direction Stop A Start?
Yes. Always tip carburetor-side up or spark-plug-side up, never air filter down. Fuel flooding the filter or cylinder causes hard starts.
Do I Need Premium Gasoline?
Regular octane is fine for most mower engines. What matters is freshness and the ethanol percentage.
Primer Bulb Vs. Choke—What’s The Difference?
A primer squirts fuel into the throat; a choke restricts air so the mix enriches. Both aim for the same cold-start goal.
How Long Can Gas Sit In The Tank?
Plan on 30 days during hot months. With stabilizer, you can stretch it to the off-season, but a spring drain is still smart.
Model And Engine Numbers?
Look for the mower’s model tag on the deck or rear frame, and the engine’s code plate on the blower housing or valve cover. Jot down model, type, and code before shopping for parts; spark plugs, filters, and blades are sold by those IDs. A phone photo saves time at the counter.
When To Seek Service
If you’ve restored fresh fuel, air, and spark and the mower still won’t start, compression or a deeper ignition fault may be in play. A leak-down or compression test will tell the story. Broken flywheel keys, failed coils, and worn rings are best handled by a shop—or by replacing a tired engine. Keep your receipts and record model, type, and code stamped on the engine shroud to speed parts lookup.
Resource Links
Briggs & Stratton’s step-by-step mower start guide
EPA guidance on E15 labeling and nonroad engines