How to Fix a Mower That Won’t Start

Honda Push MowerAre you having trouble getting your mower to start? Does it run fine for a while, then shut off when it warms up? This guide will help you located and troubleshoot common problems that can keep your mower’s engine from starting and running.

Before You Begin

If the engine was running, it could stay hot for up to half an hour. Give the mower some time to cool down, and avoid touching the exhaust and cylinder head.

Disconnect the spark plugs. When working on your engine, there’s always a chance that bumping the blade, driveshaft or starter will start the engine.

When tilting walk-behind mowers, keep the carburetor pointed up. If you flip the mower the other way, the gravity-fed fuel system will flood the carburetor.

Oil

Professional and high-end consumer engines from Honda, Briggs & Stratton, Vanguard, Subaru and Kohler have built-in shut-off switches that keep the engine from running with low oil. If a float inside the crankcase gets too low, it will cut the ignition. If the engine won’t start or shuts off suddenly, make sure it has plenty of oil.

The oil level isn’t measured the same way in all engines. All dipsticks that push into the filler neck should be fully inserted to get an accurate reading. On most engines, the dipstick needs to be inserted but not screwed in to get an accurate reading. Some Briggs & Stratton engines have a dipstick that needs to be fully threaded into the fill port to get an accurate reading.

Fuel

Does your carburetor have a priming bulb? You should feel and hear gas squirting when you push the bulb. If it doesn’t want to prime, you may need to rebuild your carburetor to get a tight seal.

Only use automotive gasoline with a maximum of 10% ethanol or 5% methanol. Higher amounts of ethanol will lean out the air/fuel mixture, while methanol will damage the fuel system.

Modern fuel goes stale quickly. Kawasaki recommends draining fuel from their engines if they are stored for more than 30 days. Other manufacturers recommend draining fuel after 30 days if it’s untreated, or 90 days if it was treated with a stabilizer.

Stale fuel can clog the engine’s fuel system, causing corrosion or leaving behind varnish that freezes components in place and clogs lines and valves. Give the carburetor, tank and fuel lines a thorough cleaning to remove these deposits.

Spark

Your mower’s engine needs a good spark to ignite the fuel. Check the spark plug wires, making sure they’re solidly connected to the plugs. Remove the spark plugs and check their condition and gap. Replace the plugs if they’re fouled or damaged.

To test the coil, remove the spark plug and connect it to the wire. Hold the end of the plug against a metal part of the engine and pull the starter. If the coil is working, you should see a spark between the electrodes.

Air Filter

A clogged filter will keep the engine from getting the air it needs to run. Clean paper filters by striking them against a hard surface. This loosens surface dirt without clogging the surface pores on the filter.

Wash foam filters in soapy water and let them dry. Check your manual for full cleaning instructions: some filters need to be soaked in oil, while others should be left dry.

Wipe out any dirt inside the air box before reinstalling the filter. Vortex separators used on commercial engines gather dirt quickly and need frequent cleaning.

Hard Pulling Starter

Check the deck for debris and clumps of grass that may be jamming the blade. Removing these blockages and cutting away grass wrapped around the crankshaft is usually enough to free the engine.

A flooded engine will be hard to turn over. Remove the spark plug, place a rag in front of the spark plug hole, and pull the starter a few times. This will push out any oil or gas in the combustion chamber.

Operator Presence Switch

Modern mowers have a switch that either cuts the ignition or applies a flywheel brake if the operator leaves the mower.

If you have a walk-behind mower, make sure the bail is pulling the attached cable tight when closed. Some handles have two holes, letting you reposition a stretched cable to take up the slack. On other mowers, you’ll need to replace the cable once it’s loose.

If you have a riding mower, make sure the seat and footplate are locked down. This can prevent the switches from activating when you’re in the seat.

Get the Parts and Service You Need to Fix Your Mower

No matter what powers your mower, you can get the parts and help you need for your mower at Shank’s Lawn Equipment. We’re an authorized dealer for all major engine brands including Honda Engines, Kohler Engines, Kawasaki Engines USA, Briggs & Stratton, Vanguard and Subaru Power.
Our shop is at 4900 Molly Pitcher Highway in Chambersburg, PA. We’re just one mile from I-81.

We also ship parts and accessories across the U.S. and Canada. If you need something for your mower, visit us online at www.shankslawn.com.

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