How to Turn On a Lawn Mower

A mower that sat all winter usually fails on fuel or charge before anything else. Run this check first so you are not diagnosing a machine that was never ready to start.

Gas mowers

Check the fuel and the oil. Use regular unleaded, 86 to 87 octane or higher, with no more than 10% ethanol, and never two-stroke mix in a four-stroke mower. Check the oil on a level surface with the dipstick wiped and reinserted; the level should sit between the marks. Gas degrades in as little as 30 days, which is why a mower that ran fine last fall often will not turn on in spring.

Battery and corded mowers

Push the pack in until it clicks and confirm it is fully charged. Insert the safety or isolator key. Unfold the handle and close both locking clamps. On a corded mower, connect an outdoor-rated extension cord at both ends and route it clear of the blade path.

Every type

Set the cutting height to its highest position for the first start so the blade is not fighting tall grass, clear clippings out of the deck, and check that the blade path is clear. On a rider or zero-turn, raise the deck, switch the blades off and set the brake. A robotic mower is started, stopped and parked from its app or its on-unit keypad with a PIN, or it simply follows its schedule, so there is no cord to pull.

Wear eye protection and sturdy shoes, and start outdoors only, because the exhaust gives off carbon monoxide. Start on flat ground, never a slope. On most walk-behinds the blade is turning the moment the engine starts, so start on a clear patch or an already-mowed strip.

The order of the steps changes with the machine. Find your type in the table, then read the detail for it below.

The detail behind each row of the table, in the order the machine wants it.

Gas push mower, pull-start

Open the fuel valve on models that have one and set the throttle to fast. On a cold engine, one that has sat more than about 20 minutes, try it with no primer first, because many mowers start in two or three pulls without it. If it does not catch, give the bulb one or two firm presses. If the mower has a choke lever instead of a primer, go to full choke and do not prime. Many newer gas mowers have neither, because an automatic choke handles the mix.

A warm engine, one that ran in the last 15 to 20 minutes, needs no primer and no choke and should fire on the first pull. Hold the bar against the handle, pull slowly until you feel resistance, then give one sharp pull. Ease the choke off over 10 to 20 seconds once it fires. Over-priming is the most common self-inflicted failure: you can always add choke, but a flooded engine costs a 15-minute wait.

Gas push mower, electric start

The fuel, oil and choke logic is the same, but the ignition event is a key or a button. Hold the bar first, then turn the key or push the button, and release the key to run as soon as it fires. Never crank more than about 5 seconds, and wait 10 to 30 seconds between attempts. On an engine with electronic fuel injection, turn the key to ON, wait for the fuel pump hum to stop after 2 to 5 seconds, then crank with no choke and no primer. The starter battery is separate from the engine and charges while the engine runs, so a mower that sat all winter may need it charged before the button does anything.

Gas self-propelled

The sequence is identical to the push mower with one addition: disengage the drive lever before starting. The self-propel lever is not the start control, and holding it while you pull makes the mower lurch forward. Engage the drive only after the engine is running and settled.

Corded electric

Connect an outdoor-rated extension cord at both ends, unfold the handle and lock it, and insert the safety key where the model has one. Hold the bar and press the start button. The motor and blade stop within about 3 seconds of releasing the bar, which is the brake working, not a fault.

Battery and cordless

Click the pack fully into place and insert the safety or isolator key, because many models will not run without it. Unfold the handle fully, close both locking clamps and lock the handle in one of its positions. On some models the mower will not start unless the grass catcher or the mulch plug is seated, so check the manual if nothing happens with a charged pack. Then press the safety button, pull the bail up to the handle and release the safety button; on some models the order of button and trigger is reversed, and either order works.

Riding mower and lawn tractor

Sit in the seat, set the parking brake, switch the blades off and push the throttle to full; on a carbureted engine, pushing past the detent is the choke. Turn the key to start, release it to run the moment it fires, back the choke off within 10 to 15 seconds and warm up about 30 seconds before engaging the deck. On an EFI engine, pause at ON until the pump hum stops, then crank. Below about 32°F, some engines have a cold-start throttle position; use it, then return to full throttle after it starts, or you get smoke and fouled plugs.

The brake and blade switches sit in the cranking circuit, while the seat switch sits in the running circuit. That is why a no-crank is almost always the brake not fully set or the blades still engaged, and why jumping the seat switch will not fix a mower that will not crank.

Zero-turn

Sit down, raise the deck to its highest position, put the blade switch down, move both steering bars firmly out to their locked neutral position and set the throttle to full. Push in and turn the key, never crank more than 5 seconds, wait about 10 seconds between tries and release the key to run immediately. Warm up at mid throttle, then mow at full throttle.

Robotic

Start, stop and park the mower from the app over Bluetooth within roughly 100 ft, over Wi-Fi or over cellular, or from the on-unit keypad with a PIN, or let it follow its schedule. The first turn-on after installation is a setup step in the app, not a start button on the machine.

Manual reel

There is no engine and no ignition: the act of pushing turns the reel. Turning it on means setting the cutting height and pushing it along the edge of the lawn.

Work from what you see and hear rather than from the parts list, because the symptom points at the cause faster than a guess does.

Nothing happens at all

On a walk-behind, the bar is not fully against the handle, the safety key is not in, the handle is not locked, or the bag or mulch plug is not seated. On a rider, the brake is not fully set, the blades are still on, or the battery is flat or its fuse is blown. A healthy 12 V rider battery reads about 12.6 V at rest; under about 12 V it is too weak to crank, and below 10.5 V it likely has a dead cell. Most riders use a 20- or 30-amp blade fuse near the battery or in the harness, and a replacement should match the old one, never a bigger rating.

The sound at the key is the diagnosis

• Total silence points at the battery, the fuse, a safety switch or the ignition switch.
• One loud click points at the solenoid or a weak battery.
• Rapid clicking means the battery is too weak.
• Cranks freely but will not fire means fuel or spark.

It starts, then dies the instant you let go of the bar

That is the operator presence control doing its job. The engine is designed to stop when the bar is released, so hold the bar for the whole cut.

It turns over but will not fire

Check stale fuel first, since gas degrades in about 30 days, then the spark plug connection, then the air filter.

Flooded engine

The signs are a raw gas smell, a wet plug, a mower that fired once then quit, a heavy or hydraulic-feeling pull, and black smoke. Turn the choke off, set the throttle to fast and pull 5 to 10 times, or wait 15 minutes on level ground and try again without priming.

Cord hard to pull

The deck is clogged with grass. Remove the key or the battery pack before you clear it.

Battery mower with a charged pack that will not start

Recheck the isolator key, the handle clamps and the bag or mulch plug.

When to stop pulling and take it in

Give it a handful of pulls. If it has not caught in five or six pulls with the right settings, stop and work through the list rather than pulling harder. Take the mower to a shop if the engine will not turn over by hand, if a fuse blows again immediately, or if you smell fuel or see arcing.

The stop control is the same control you hold to start. Release the bar on a walk-behind, or the bail on a battery or corded mower, and the engine and blade should stop within about 3 seconds; if they do not, stop using the mower. On a rider or zero-turn, turn the key off, set the brake and switch the blades off. Remove the key or the battery pack whenever you leave the mower or clear a clog. Knowing where the stop control is makes the starts-then-dies symptom obvious the first time it happens.

Start outdoors only, on level ground, with the blade path clear and bystanders and pets well away; battery-mower manuals put that distance at about 100 ft. Wear eye protection and sturdy shoes. Never tape, wedge or bypass a safety switch, and pull the key or the pack before any clearing or adjustment. On most walk-behinds the blade turns the moment the engine starts, so keep feet and the discharge chute clear from the first pull.