Lawn Mower Won't Start After Winter? 5 Causes and Fixes

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Last updated October 28, 2026 · Applies to: lawn mowers from Toro, Husqvarna, Honda, Troy-Bilt, John Deere and Craftsman and others

Cause 1: Fuel left in over winter turned to varnish

Step-by-step instructions for this cause are being written.

Fuel path: tank to cylinder: Fuel tank → Cap vent → Shut-off valve → Fuel filter / line → Carburetor bowl → Main jet → Intake → cylinderFuel tankfresh fuelCap ventlets air inShut-off valveopen?Fuel filter / lineno cracksCarburetor bowlfloat + needleMain jetmeters fuelIntake → cylinderfuel + air
Fuel path: tank to cylinder. Fuel must flow through every stage. A blockage at any box starves the engine.

Cause 2: Gummed carburetor bowl and jets

Step-by-step instructions for this cause are being written.

Inside a float-bowl carburetor: Fuel inlet → Needle & seat → Float → Float bowl → Main jet → Emulsion tube → Venturi / throttleFuel inletfrom tankNeedle & seatshuts off flowFloatsets fuel levelFloat bowldrain screwMain jettiny orificeEmulsion tubemixes airVenturi / throttleto intake
Inside a float-bowl carburetor. Varnish from old fuel usually blocks the main jet or emulsion tube first.

Cause 3: Corroded or fouled spark plug

Step-by-step instructions for this cause are being written.

Ignition path: magnet to spark: Flywheel magnet → Ignition coil → Stop / kill wire → Plug lead & boot → Spark plug → CombustionFlywheel magnetkey aligns timingIgnition coilair gap to flywheelStop / kill wiregrounds coilPlug lead & boottight fitSpark pluggap + conditionCombustionspark ignites mix
Ignition path: magnet to spark. Test the end of the chain first: a spark tester on the plug lead.

Cause 4: Air filter blocked by a nest or debris

Step-by-step instructions for this cause are being written.

Air intake path: Air filter cover → Pre-filter / foam → Paper filter → Carburetor throat → Intake gasket → CylinderAir filter coverclips / screwPre-filter / foamclean, oiledPaper filternot oil-soakedCarburetor throatchoke plateIntake gasketno air leaksCylinderintake valve / port
Air intake path. A restricted filter richens the mixture; a leak after the carburetor leans it out.

Cause 5: Dead battery (electric-start models)

Step-by-step instructions for this cause are being written.

Electric-start circuit: Battery → Fuse → Ignition switch → Safety switches → Starter solenoid → Starter motor → Flywheel ring gearBatterycharge + terminalsFuseblown?Ignition switchkey 'start'Safety switchesseat / brake / PTOStarter solenoidclick = signalStarter motorBendix gearFlywheel ring gearcranks engine
Electric-start circuit. Work from the battery outward with a multimeter: 12.6 V at rest is a charged battery.

Which cause is it?

The decision table is being compiled from shop pricing and manufacturer data.

Brand notes

Brand-specific notes for Toro, Husqvarna, Honda and Troy-Bilt are being researched.

When to take it to a shop

Hand it over if the engine still will not run after the fuel, spark and air checks, if you find metal in the oil or the engine is seized, or if the machine is under warranty (opening it yourself can void it).

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Frequently asked questions

Answers being written: Do I need to drain the gas after winter? · Why won't my mower start in spring? · Can old gas damage a mower? · How do I prevent this next winter?