9 Fixes For When Your Lawn Mower Won’t Start

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Lawn care can be tedious, but come springtime, mowing becomes a fact of life for many folks. When you tackle that first cut of the season, however, there are few sounds as disheartening as that of a lawn mower engine that turns over but doesn’t start. You’re probably wondering why your lawn mower won’t start after winter. Before you drag the mower in for repairs or invest in costly replacement parts, look for a few potential problems that you can probably fix fairly easily. “The most common reasons for a lawn mower not starting are often mechanical, especially if the mower has been sitting for a while,” says Ryan Farley, CEO of LawnStarter, an online service that connects homeowners with local lawn care providers. Any one of the concerns below could be the culprit; check out this list and implement the right fix to your problem. 1. Clean and refill the lawn mower fuel tank. Photo: istockphoto.com An obvious—and often overlooked—reason your mower is not starting is that the tank is empty or contains gas that is either old or contaminated with excess moisture and dirt. “Are you using fresh fuel that’s less than 30 days old?” asks Shawn Carothers, Senior Marketing Manager at Toro, who says this is a common issue homeowners encounter. If your gas is more than a month old, use an inexpensive oil siphon pump to carefully drain it from the tank into a gas can. Be sure to dispose of old gas correctly. 2. Clear the mower deck of debris. Photo: istockphoto.com The mower’s deck prevents grass clippings from showering into the air like confetti, but it also creates a place for them to collect. Grass clippings can clog the mower deck, especially while mowing a wet lawn, preventing the blade from turning. “Spray the deck, remove and clean the blades, and if necessary, scrape off grass clumps and organic matter that won’t loosen with water,” says Carothers. “Wipe the mower down to ensure it is dry.” If the starter rope seems stuck or is difficult to pull, then it’s probably due to a clogged deck. With the mower safely turned off, tip it over onto its side and examine the underbelly. If there are large clumps of cut grass caught between the blade and deck, use a trowel to scrape these clippings free. When the deck is clean again, set the mower back on its feet and start it up. 3. Change the lawn mower air filter. Photo: istockphoto.com Your lawn mower’s air filter guards the carburetor and engine from debris like grass clippings and dirt. When the air filter becomes clogged or too dirty, says Carothers, it can mean the lawn mower won’t crank. To keep this from happening, replace paper filters—or clean or replace foam filters—after every 25 hours of engine use. The process for removing the filter depends on whether you are operating a riding or walk-behind lawn mower. If a riding mower is part of your lawn care routine, turn off the engine and engage the parking brake; for a walk-behind mower, pull the spark plug wire from the plug. Then, lift the filter from its housing. The only choice for paper filters is replacement. If you’re cleaning a foam filter, wash it in a solution of hot water and detergent to loosen grime. Allow it to dry completely, and then wipe fresh motor oil over the filter, replace it in its housing, and power up the mower—this time to the pleasant whirring of an engine in tip-top condition. 4. Check the spark plug. Photo: istockphoto.com Is your lawn mower still being stubborn and you’re still wondering “Why won’t my lawn mower start?” The culprit may be the spark plug, which is responsible for creating the spark that ignites the fuel in the engine. If it’s loosened, disconnected, or coated in water or carbon residue, the spark plug may be the cause of your machine’s malfunction. Locate the spark plug, often found on the front of the mower, disconnect the spark plug wire, revealing the plug beneath. Use a socket wrench to unscrew the spark plug and remove it. Check the electrode and insulator. If you see buildup, spray brake cleaner onto the plug, and let it soak for several minutes before wiping it with a clean cloth. Reinstall the spark plug by hand Then use a socket wrench for a final tightening. If the problem persists, consider replacing the spark plug. 5. Make sure the fuel filter is clear. A clogged fuel filter is another possible reason a lawn mower won’t restart. When the filter is clogged, the engine can’t access the gas that makes the system go. If your mower has a fuel filter (not all do), check to make sure it’s functioning properly. First, remove the fuel line at the carburetor; gas should flow out. If gas does not flow out, confirm that the fuel shutoff valve isn’t accidentally closed. Remove the fuel line that’s ahead of the fuel filter inlet. If gas runs out freely, there’s a problem with the fuel filter. Consult your owner’s manual for instructions on replacing the filter and reassembling the mower. Use a fuel stabilizer to extend the life of the gas and prevent future buildup. 6. Clear the vent in the lawn mower fuel cap. Photo: istockphoto.com The mower started just fine, you’ve made the first few passes, then all of a sudden the mower quits. You pull the cord a few times, but the engine just sputters and dies. What’s happening? It could have something to do with the fuel cap. Most mowers have a vented fuel cap. This vent is intended to release pressure, allowing fuel to flow from the tank to the carburetor. Without the vent, the gas fumes inside the tank begin to build up, creating a vacuum that eventually becomes so strong that it stops the flow of fuel. To find out if this is the problem, remove the gas cap to break the vacuum, then reattach it. The mower should start right up. But if the lawn mower won’t stay running and cuts off again after 10 minutes or so, you’ll need to get a new gas cap. 7. Inspect the safety release mechanism cable. Photo: istockphoto.com Your lawn mower’s reluctance to start may have nothing to do with the engine at all but rather with one of the mower’s safety features: the dead man’s control. This colorfully named safety bar must be held in place by the operator for the engine to start or run. When the bar is released, the engine stops. While this mechanism cuts down on the likelihood of horrific lawn mower accidents, it also can be the reason the mower won’t start. The safety bar of a dead man’s control is attached to a metal cable that connects to the engine’s ignition coil. “If this cable is damaged, stuck, or improperly adjusted, it can prevent the safety interlock from disengaging when the handles are squeezed, not allowing the mower to start,” says Carothers. “Always ensure this cable has free movement and isn’t binding.” If the cable cable is damaged or broken, you’ll need to replace it before the mower will start. Fortunately, replacing a broken control cable is an easy job. You might be able to find a replacement cable at a home improvement center, though don’t be surprised if you have to jot down the serial number of your lawn mower and order the part from the manufacturer’s website. 8. Check to see if the flywheel brake is fully engaged. The flywheel helps to make the engine work smoothly through inertia. “If your mower is refusing to start, or throws spark into the combustion chamber at the wrong time, it could be because of a misaligned flywheel,” says Carothers. If the flywheel brake is fully engaged, it can make a mower’s pull cord hard to pull. Check the brake pad to see if it makes full contact with the flywheel and that there isn’t anything jamming the blade so the control lever can move freely. If the flywheel brake’s key sheared, the mower may have run over something that got tangled in the blade. It is possible to replace a flywheel key, but it does require taking apart the mower. 9. Consider less-common reasons a lawn mower won’t start. Photo: istockphoto.com Carothers offers some more unusual reasons a lawn mower won’t start: There’s an ignition switch malfunction. The switch may be faulty or not making proper contact. There may be water in the fuel line. This can prevent the fuel from combusting during the starting process. Incorrectly adjusting the choke can lead to either too much or too little fuel mixing with air in the engine, preventing it from starting. Low oil levels or old oil that has broken down can lead to increased friction and ultimately may make starting more difficult. Look out for signs that the mower needs professional repairs. Photo: istockphoto.com While repairing lawn mowers can be a DIY job, there are times when it is best to ask a professional to repair a lawn mower. If you’ve done all of the lawn mower maintenance recommended by the manufacturer, and gone through all of the possible ways to fix the mower from the steps above, then it may be best to call a pro. Here are a few signs that indicate when a pro’s help is a good idea. You see black smoke. The engine will benefit from a technician’s evaluation, as it could be cracked or something else might be worn out. Excessive oil or gas is used. If you’ve changed the spark plugs, and done all of the other maintenance tasks, and the mower is consuming more than its usual amount of oil or gas, consult a professional for an evaluation. The lawn mower is making a knocking sound. When a lawn mower starts making a knocking sound, something could be bent or out of alignment. It may be tough to figure this out on your own, so a pro could help. A vibrating or shaking lawn mower can be a sign of a problem beyond a DIY fix. Usually something is loose or not aligning properly.