The Ultimate Beginner's Guide

To Lawn Mower Maintenance

Common Types of Engine Issues

There are lots of things you'll need to troubleshoot with your lawn mower, beginning with your engine. 

It Won’t Start

This is probably the easiest issue to notice.  You pull the cord five (or fifty) times—and the mower still doesn’t start.

The first things to check are whether the mower is filled up with fuel and oil (if it’s a gas mower), if it has enough charge in its battery (if it’s a cordless electric), or if it is plugged in and turned on at the wall (if it’s a corded electric).

Even though those seem simple, you’d be surprised how often you can forget to do those crucial first steps.

If you’re using a gas mower, think about when the last time you changed the fuel was. Letting fuel sit in the mower or in a container for a long time can mean it’s no longer as effective. 

You’ll also want to make sure that if your mower has a fuel tap, it’s turned on. And double check that the wire connecting the spark plug is firmly in place.

Gas mowers also need a functional air filter to allow oxygen in, otherwise they can’t burn their fuel. You should check that your air filter is in good order, and hasn’t been clogged by dust or fuel.

If none of these work, it’s possible that you could have a flooded engine on your hands. This occurs when fuel saturates the spark plug, meaning it can’t ignite properly.

Engines typically flood due to overuse of the choke when trying to start the mower, so this is a problem that is more likely to occur on a cold morning. A flooded engine is also often accompanied by a smell of fuel, so if your mower smells more like petrol than usual you might want to consider this as a possibility.

Luckily, a flooded engine is easy to fix—just let the mower sit for fifteen minutes. This should allow the carburetor to dry out enough to start the mower again.

There are faster ways to fix a flooded engine, but these require disassembly of the mower itself.  You can remove the air filter and spark plug to allow a faster rate of drying if you're in a rush.

It Overheats

An overheating motor is certainly alarming, and it can impact the performance of the motor as well as pose a danger to you while you are using it.

Overheating motors are caused by multiple issues, but the most obvious is blocked or damaged cooling fins.  

These are typically attached to the engine, and you’ll need to remove a significant portion of the mower to get at them.

Remove the exterior covers and casings, and then clean the cooling fins with a rag or similar item.

Although it can be tempting to use compressed air, this has the risk of blowing any debris further into the mower rather than further out of it- which is definitely not the aim!

It’s also possible that your mower has run out of oil, as the function of oil is to lubricate parts and reduce friction.  Make sure that you’ve topped up the oil sufficiently after the mower has cooled down.

Finally, an overheating motor can also be caused by using the wrong fuel or the incorrect spark plug. Check out the fuel system issues section for what to do to fix the incorrect fuel.

If you suspect the issue is an incorrect spark plug, check your manual to confirm the spark plug you have installed is the right one for your mower.

Common Types of Pull Cord Issues

It Pulls Too Easily… And Doesn’t Work

You’re yanking the pull cord over and over again, and it just won’t work. What’s more: where you’d normally expect a little effort to be required, it moves as though it’s completely loose.

This likely indicates that you have a damaged mechanism around your mower’s pull cord. This could be a damaged pulley system or damaged pawls, which are the small wings attached to the pulley that help to start the engine.

In order to access these components, you’ll need to remove the cover on top of the pull cord entry, then detach the pull cord section from the rest of the motor.

It Doesn’t Pull At All

The opposite of the previous problem, this doesn’t necessarily mean something is directly wrong with the pull cord array.

Although the pulley and pawls could be jammed, it is also possible that the mower blade is jammed, or that the engine has seized.

You should first check the externally accessible parts of the mower for obvious blockages, such as the blade.

It Breaks

Don’t worry! Replacing a pull cord isn’t too difficult.

There are plenty of videos available online, and likely instructions for replacement in the manual for your mower.

You’ll need to pull out the old cord, and replace it with a new one.  Make sure to note how long your original cord was so that you can calibrate the winding mechanism while replacing it.

Never put your fingers near the blade unless you are sure the mower cannot start.

If there are no obvious blockages in these areas, you should check that the pulleys are turning smoothly and that the pawls are not stuck on anything inside the motor.

Common Types of Deck Issues

The Lawn Mower Does Not Cut Evenly

Maybe you’ve managed to finish cutting your lawn, but you notice that there are strips of it that seem not to have been cut quite as well as others.

However, you know the blade has been working the whole time—because you’ve heard or seen it, after all!

In that case you likely have an issue with the positioning of your deck, which is the part of your lawn mower that supports the blade and safety shields.

It’s possible that the deck is on an angle, or has been lowered or raised too much.  

Adjusting the deck can be relatively easy depending on your mower’s design, so check your manual to see what you can do.

The Lawn Mower Does Not Cut Well After Several Uses

It’s possible that you’ve worn out another part of your motor (such as the blade). However, it could also be that the issue is a much less expensive deck fix.

Sometimes the deck can become clogged with grass, especially if you don’t clean it well after each use.

If this happens, the deck will not be held in the correct place relative to the grass you’re trying to cut at a given time, and as a result your mower won’t cut well. Make sure to clean out the grass and try it again. 

Be careful near the mower’s blade, and remove all possible causes of engine ignition (spark plug, cord, or battery).

It’s also possible that the mower’s tires have deflated- or even that they have been overinflated, leading to a poor cutting position for the deck.

This can be fixed by letting out some air or putting more in. Check your manual for instructions on how to do this, and be careful not to overfill and pop the mower’s tires.

Common Types of Blade Issues

Warning: only interfere with the blade if you are confident in what you are doing.  Do not touch the blade with your hand if you can avoid it. Disconnect the spark plug/power cord/battery before working with the blade.

It Doesn’t Spin

This is probably the most obvious type of blade issue to diagnose.  It often comes hand in hand with the mower refusing to start.

If you’ve tried some other troubleshooting techniques for a non-starting mower as listed above and haven’t had any success, it’s possible you have an issue with the blade.

If the blade is clogged and can’t turn, the mower won’t start!

Make sure that the blade is debris-free by using a stick or other long implement to gently attempt to rotate the blade. Scrape anything out that is jammed between the blade and the deck.

If you haven’t used the mower for a long time (or it’s a second hand model), it’s possible that the blade may have rusted onto its axel.  Check for any obvious signs of rust.

It Doesn’t Cut

The blade spins, alright—but when you push it over grass, nothing happens.

This is often similar in presentation to an issue with your mower’s deck height, as a too-high deck will mean the blade can’t reach the grass to cut it. Make sure this is not the issue first.

If you’re sure it’s not the mower deck, and the blade spins, it’s likely that your blade is blunt. You may need to sharpen the blade or replace it entirely.

It Cuts Unevenly And/Or Makes An Odd Noise

This is a sign that your blade may be loose.  A rattling noise is a particularly obvious symptom of a loose blade, as are any drag marks in the grass or soil from the blade touching the ground.

You’ll need to tighten the blade before you continue using your mower, as a loose blade can fall off the mower- posing a danger to you.

This can typically be done with a wrench or similar device, and will require that you prop up the mower so you have access to the bottom.

As always, ensure the mower is disconnected from power (if electric) or has the spark plug removed (if petrol) before beginning maintenance.  Take extra care to avoid cutting yourself on the stationary blade.

It will likely be necessary to hold the blade still while tightening it. Don't use your hand for this—wedge something that won't damage the blade into the gap between it and the deck, such as a firm cushion or bundle of newspaper or rags.

Common Types of Drive System Issues

These issues are only applicable to self-propelling mowers, where they have a drive motor that propels them around.

The Drive System Isn’t Engaging

This is an easy problem to diagnose—your mower will feel a lot heavier and more difficult to move, and may not roll smoothly at all.

The first thing to do is to check the driving wheels of your mower. Depending on the model you have, these will either be at the front or the rear, and you should consult your manual as to which end is relevant.

If they are clogged (for example with grass clippings), this may be the issue. Removing the clog may allow them to rotate freely and function again.  

Be careful when removing any blockage and ensure that the drive system is turned off so that your fingers aren’t caught in the wheel.  

Use another instrument (such as a pole or rake) if you can to remove the blockage.

If this isn’t the issue, it’s time to take a look at the system attached to the drive wheels. You can typically remove the drive wheels with a normal screwdriver or wrench.

If any of the gears behind the wheels look obviously damaged or don’t turn freely, this is likely the cause of the issue. You will normally have to replace these gears completely.

The Drive System Isn’t Responding To Input, But Is Running

This is definitely one of the most unnerving faults in your drive system.

The good news is that you can typically still turn off the mower by turning off the throttle or releasing the lever.

If you can’t adjust the speed while your motor is running as you should be able to, you may need to check any electric systems linking the controller to the drive motor, as well as inspect the gearbox to ensure that the gears are changing smoothly.

Common Types of Fuel System Issues

Fuel Buildup/Blockage

If you’ve left your mower full of fuel for a long period of time, the fuel has likely partly evaporated—leaving only a gunky residue behind.

This residue can block fuel lines, the carburetor (which is responsible for mixing air and fuel in the correct proportions), or the engine itself.

If this has occurred, the best thing to do is to clean the engine with a specialized cleaning agent, such as a carburetor cleaner.

You can also prevent this by using specific kinds of fuel that do not evaporate as quickly, or by adding fuel stabilizers to your existing fuel supply.

I Put The Wrong Fuel In…

Don’t worry! Unlike putting the wrong fuel in your car, this is a relatively easy fix considering the mower is much smaller and easier to disassemble and drain.

Of course, you ideally identify this problem before you attempt to start the mower.  If you have already started the mower, draining it is a good first step, but you may need a professional to repair it fully.

Draining the mower and ensuring that the fuel tank and fuel system lines are wiped clean of any fuel residue will allow you to remove any of the incorrect fuel, and hopefully have you ready to mow again in no time!