Updated on May 15, 2023
Tired of feeling helpless when something goes wrong with your lawn mower? Learn gas and electric lawn mower troubleshooting for these common problems.
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This is an easy one to troubleshoot. If it turns over but your mower won’t start, chances are you’ve got stale gasoline in the tank or the carburetor bowl. Gas goes stale after sitting for a while. So if you’ve just taken your mower out of winter storage and didn’t drain the tank before putting it away, bad gas is likely the problem.
Luckily, it’s simple to fix. Drain the old gas from the tank, then unbolt the carburetor bowl and drain the gas inside into a cup or container. Shoot a little carb cleaner into the bowl, then add fresh gas. Chances are, your mower will start up.
The simplest and most likely cause here is a bad, dirty or loose spark plug. If the plug is oily, caked with gunk or poorly connected, your engine won’t start.
Disconnect the spark plug wire, then remove and inspect the plug. Clean any oily residue you find with rubbing alcohol and remove any black carbon buildup with a small wire brush. Or simply buy and install a new spark plug.
Most likely, a clogged carburetor is the culprit. The residue left behind by stale gas can restrict flow through the carburetor, leading to a stalled engine. Remove the carburetor and clean it, then replace the stale fuel in the tank. If it still doesn’t start, then you might need to replace the fuel filter of your lawn mower.
Another possibility is a clogged fuel cap. Look for small vent holes that allow air into the gas tank as fuel is consumed. If they’re blocked by grass or other debris, the resulting vacuum will make the engine stall.
Most of the time, this means a stuck or “frozen” pull cord that won’t budge when you tug on it.
Many push mowers come with a swiveling plastic flap at the back to stop grass and other debris from flying out. If this folds forward beneath the mower, it can prevent the blade from rotating when you pull the cord to start up. Simply lift the mower, fold the flap back where it belongs, and all should be well.
If that’s not the problem, pull cord replacement is always an option.
If your push lawn mower starts smoking, it’s probably burning oil. If you’ve recently changed the oil, you may have overfilled the reservoir. Some oil may be dribbling out on a hot part of the engine, where it’ll burn off and smoke. Draining a little oil out will solve the problem.
Another cause is a piston ring malfunction, leading to oil leaking and burn. New piston rings are easy to install.
If your mower slows noticeably during use, check the blade. Any buildup of dirt and grass clippings can restrict the blade’s movement, causing the engine to work harder.
Shut off the mower, disconnect the spark plug wire, then turn the mower over. Clean dirt and grass from the blade and underside of the mower deck.
Another possibility is a dirty air filter. Dust and debris can restrict air as it moves through the engine, leading to improper combustion and loss of power. Fix this by cleaning or replacing the air filter.
Sometimes a lawn mower will start and run just fine, but won’t turn off when you release the blade control handle. This is often caused when the mower’s switch stop tab doesn’t contact the control bracket when you release the handle. Chances are the mower took a hard impact at some point, knocking these two parts askew.
The fix is easy as long as you know where to look. Remove the protective shroud from the top of the engine, then find the switch stop. (Refer to your owner’s manual if you’re unsure.) Grab a screwdriver and gently bend the switch stop downward until it touches the control bracket. Once that’s done, your mower should shut off just fine.
Most times when I’ve dealt with a lawn mower that burns too much gas, it’s because of a dirty air filter. Air filters allow a specific amount of air into the engine to create the gas-air mixture needed for proper combustion. If your engine is running too rich, chances are there’s a dirty filter restricting air flow, causing it burn more gas and less air than it should.
Remove the air filter and give it a good cleaning with an air compressor, or simply buy and install a new one.
Every time I’ve had a lawn mower overheat, it’s been due to a dirty engine.
Air passages run through the engine to cool it. When these become clogged with grass clippings and other debris, your engine won’t have sufficient air flow to cool itself during use and could easily overheat. Let it go too long and you risk serious damage to your mower.
Remove the mower’s protective shroud, then clean out all passages with an air compressor and spray attachment.
Ragged cuts indicate a dull or damaged mower blade, but not cutting grass at all is a different story. If that’s the case, your blade was installed incorrectly — probably upside down.
Disconnect the mower’s spark plug, then check the blade. The upturned wings should face toward the mower deck. If not, remove the blade and flip it over.
Every so often, your lawn will look ragged and unkept after mowing rather than short and neat. When this happens, a dull blade is almost certainly the cause.
Disconnect the spark plug, then flip the mower upside down. Remove the blade with a socket wrench, then examine the edge. If it seems dull or corroded, purchase and install a properly sized replacement. Or if you’re good with a grinder, you can sharpen the blade yourself. Just be sure to wear gloves, eye protection and hearing protection.
A push mower that vibrates excessively while running could have a bent, cracked, broken or unevenly sharpened blade. If you’ve hit something hard with your mower or sharpened the blade recently, there’s a decent chance your blade is now unbalanced. This throws the rotation of your engine out of whack and leads to all sorts of unwanted movement.
Disconnect the spark plug, then inspect the blade. If it’s cracked, broken or bent, replace it immediately. If you sharpened it recently, hang it on a nail by the central hole and see if it dips to one side or the other. Even it up on your grinder until it sits level.
