Lawn mower not running. 9 Reasons Your Mower Stopped Running: SOLVED

Reasons Your Mower Stopped Running: SOLVED!

My son just called me pretty upset his lawn mower stopped running. He’s a new homeowner and has received a lot of hand-me-down yard tools including a lawn mower.

They aren’t in the best condition. He can’t complain too much when the equipment he receives is free, but he still does when they stop working!

A mower will stop running when it isn’t getting air, fuel, and spark required for combustion.

This may be due to old fuel, a clogged air filter, a dirty carburetor, clogged fuel lines, a bad fuel cap, or insufficient engine oil.

With so many reasons a lawn mower can stop running, I have listed possible running problems starting with the easiest and most common issues and ending with the tougher, harder-to-fix, issues. Hopefully, your problem is in the “easier to fix” category.

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Follow all safety instructions provided in your equipment operator’s manual before diagnosing, repairing, or operating. Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.

Reasons Your Lawn Mower Stopped Running

No fuel in the Gas Tank

So, when I asked my son if he checked for gas in the gas tank, he just sighed and wondered if I thought he wasn’t very Smart. He said, of course, he checked the fuel level. I asked because it is such a simple solution that it is often overlooked.

Fill your fuel tank with unleaded gas with an octane rating of 87 or higher. You can find this information on the label on the gas station’s fuel pump.

87 octane is commonly known as regular gas. Make sure your gas contains no more than 10% ethanol content.

Bad or Stale Fuel

Now that you have confirmed you have fuel in the gas tank, you need to figure out if you have bad gas that degraded and broke down becoming less effective.

Gasoline only has a shelf life of about 30 days so it’s important to use gas within 30 days before it starts to degrade.

If you are unable to use your fuel within 30 days, add a fuel additive to stabilize your gas. I like a product called Sea Foam that can be purchased online or at your local automotive store.

You can read more about the advantages of using Sea Foam in my article.

Much of today’s fuel contains ethanol which is an environmentally friendly corn-based product. While gas with ethanol is okay to run in your vehicle, it is not good for your lawn mower engine.

Ethanol attracts moisture that can collect in your fuel system.

This moisture, when evaporated, can gum up your fuel system and cause you to have problems with your lawn mower running.

This is why small engine manufacturers recommend using fuels with no more than a 10% ethanol level. A lower level of ethanol content or fuel without ethanol is best for the longevity of your fuel system.

Drain your fuel tank and fill it with fresh gas. Add Sea Foam fuel treatment to your gas. Sea Foam acts as a fuel system cleaner and stabilizer.

Dirty Air Filter

An air filter prevents lawn mower engine damage by preventing dirt and debris from entering the engine intake. While the air filter acts as the first line of defense to protect the engine, if it becomes plugged, it can hurt the engine.

When the engine isn’t able to get clean air because the filter is plugged, it will search for air wherever it can find it. This may cause your engine to overheat and pull air and oil out of the crankcase.

Check your air filter regularly and clean or replace your air filter as needed.

Clean Paper Air Filter Element

Remove the filter from the air filter housing. Use a clean cloth to remove any dirt left in the housing. Be careful not to let any dirt enter the air intake.

Tap the filter against a solid surface to knock the loose dirt from the filter. Hold the filter up to the light to verify you can see light through the filter. If you are unable to see light you must replace the air filter.

Clean Foam Filter Element

You may have a foam filter. Remove the filter from the air filter housing making sure you don’t knock any dirt into the intake.

Wipe out any dirt left in the housing with a clean cloth. Wash the foam filter with dish soap removing any dirt and oil on the filter.

Rinse the filter until all soap is removed and let air dry. Use filter oil to lightly coat the filter. Squeeze the filter of any excess filter oil. You do not want your filter to be over-saturated with oil.

If your air filter has dark spots on it or has become dry and brittle, you need to replace your foam air filter.

Clogged or Broken Fuel Cap

Fuel caps must have a vent. Without your fuel cap properly venting, the fuel tank will form a vacuum and fuel will be unable to flow from the tank.

You can check if your cap is causing your lawn mower to stop running by removing the cap and letting your lawn mower run. If it runs well, replace the cap and continue to let the engine run to see if the engine starts running sluggish or turns off.

If this happens, chances are your fuel cap is bad and you need to replace it with a new one if you are unable to unclog the vent.

Dirty and Clogged Carburetor

Gummy and hard deposits from running bad fuel through your lawn mower can buildup up in the carburetor. A carburetor regulates the amount of fuel and air required to create combustion.

A dirty carburetor is not able to allow fuel to flow through the stem to the carburetor jet.

Spray carburetor cleaner into the air intake and start your engine. If it doesn’t stay running, you will need to clean your carburetor or replace it. Read this article for steps to clean your lawn mower carburetor.

Plugged Fuel Filter or Fuel Lines

Much like deposits left by fuel can clog parts of your carburetor, it can also clog your fuel filter and fuel lines. If your fuel filter is dirty and clogged, you must replace it.

Use clamps to stop fuel flow and remove fuel lines to check for fuel flow. You can clear clogged lines by spraying carburetor cleaner into the line and then using compressed air to blow the line to remove clogs.

When fuel lines become dry and cracked, or you are unable to remove a clogged line, they can easily be replaced.

Visit your hardware store or lawn mower dealership with the correct diameter and length of fuel hose required.

Too Much Engine Oil in the Crankcase

Adding too much oil to your lawn mower can cause your engine to smoke and stop while mowing. The smoke can clog your air filter causing your engine to look elsewhere for air and causing your lawn mower to stop running.

Too much oil in your lawn mower can cause significant damage including internal engine damage and the possibility of having to replace your engine

Remove excess engine oil until you are at the correct oil fill line on the dipstick following your manufacturer’s guidelines. Use one of these methods to remove engine oil.

• Drain Plug – Loosen the drain plug and then quickly tighten it back up to only allow a small amount of oil to drain.
• Remove Engine Oil Filter – You can drain a little oil out of the air filter. Spin off the filter. Have a cloth ready to collect oil.
• Oil Evacuator – Vacuum the oil through a tube placed in the oil fill.
• Turkey Baster – This simple kitchen tool can easily suck a small amount of oil. Do not reuse it for food purposes after using it with your engine oil.

Too Little Engine Oil in the Crankcase

When your engine oil is low, your engine doesn’t have enough lubrication to run sufficiently. Friction begins to build, creating heat that can melt internal engine components. This heat can prevent your lawn mower from running.

Look over your engine for oil leaks. You can try to change the engine oil and filter, but when the engine overheats and stops running chances are adding engine oil isn’t going to help.

You probably have bigger problems with internal engine damage.

You will need to bring your mower to your local small engine repair shop so your engine can be looked at for internal engine damage.

Engine Overheats

Anytime an engine overheats your lawn mower stops running. This can include using the wrong type of oil, clogged engine fins or housing, or your engine working harder due to cutting conditions.

Read more about lawn mower overheating causes in “7 Things That Can Cause a Lawn Mower to Overheat”.

Still Having Problems with Your Lawn Mower?

Lawn mower ownership doesn’t come without its frustrations. Own a mower long enough, you are bound to run into many lawn mower problems including starting, smoking, leaking, cutting, and overheating.

For mower troubleshooting, check out my guide Common Lawn Mower Problems: Solved.

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Lawn Mower Doesn’t Run At Full Speed – 7 Causes

Lawnmowers have small engines that do not produce a lot of power.

However, they are highly efficient for cutting grass.

Proper care and regular maintenance will help sustain the performance of any type of lawnmower.

If your lawnmower doesn’t run at full speed, here are 7 causes that might be affecting it and the solutions to get it back up and running.

They operate in outdoor areas where they are exposed to dirt, debris, and moisture.

All of which can significantly damage their engines and cause a multitude of operational issues.

A slow run is one such outcome. It is a common problem that can be caused by various things.

Fortunately, most lawnmower issues can be easily fixed at home, at a fraction of the price of professional services.

It is essential to switch off machines and ground spark plug wires before carrying out any lawnmower maintenance.

Common Problems That Make Lawn Mowers Run Slowly

Disengaged Or Damaged Drive Belt

In lawnmowers, drive belts transfer power from the engine shaft to the transmission.

The transmission then propels the wheels forward (or backward) and also spins the blade.

When lawnmowers move slowly, the issue is usually caused by a dislodged or damaged drive belt.

Solution

The following details are explained in the owner’s manual. Turn off the lawnmower and access the drive belt. Reattach it, if it is dislocated, or replace it, if it has damage.

Clogged Spark Plug, Air Filter, Or Carburetor

Clogging is a common occurrence in most engine parts.

When blockages occur in the spark plug, air filter, and carburetor, mainly, the speed of a lawnmower can be greatly reduced.

They are essential units that affect performance.

Solution

Dirty elements must be cleaned, and damaged ones must be replaced.

Spark plugs and air filters are easy to clean by adhering to instructions laid out in owners’ manuals.

Remove the spark plug from the lawnmower using a socket twist and clean it using a brake cleaner. If the top of the spark plug is black, replace the spark plug.

Additionally, they are readily available and cheap to replace when blockages cause damage.

Carburetors are more expensive to replace, but they can be cleaned and rebuilt when clogging has not caused extensive damage and corrosion.

Petrol Blend

Different fuel providers sell different types of petrol blends. Fuels mixed with ethanol are some of the most popular.

They are cost-effective and environmentally sustainable.

FIX Engine Surging on any small engine QUICKLY

The different varieties of fuel cause minimal damage to car engines.

However, they can cause a lot of destruction to the smaller and less robust engines of lawnmowers.

This can lead to poor performance and a slow engine pull.

Solution

Contact the lawnmower supplier or check the manual for details on the best petrol blend to use.

Only use fuel suppliers that offer the particular blend required.

Additionally, if using the wrong fuel damages any engine parts, they must be replaced before switching to the correct blend.

Stale Petrol

After a month, petrol begins to break down due to exposure to air and other environmental factors.

Some of its compounds evaporate, and it becomes thicker.

This makes it lose a lot of its combustibility so that petrol lawnmowers will run slower.

Solution

Old petrol must be drained from a lawnmower and replaced with fresh fuel.

A fuel stabilizer can also be mixed in with petrol to extend its stability.

It is essential to know that petrol left within a storage container also gets bad after a month.

It must not be used to refill lawnmowers.

Old Battery

Cordless lawnmowers often become slower as their batteries age.

Old batteries will not have enough power to drive a machine at high speed, even after a full night’s charge.

Solution

If a lawnmower has reduced power after a battery has been charged all night, it needs to be replaced.

Cutting Tall Grass

If your grass is too tall for your lawnmower’s cutting blade, the grass can get tangled up in the blades and slow down movement.

Solution

Most lawnmowers have multiple cutting heights. Often between 2.5 to 4 inches

The cutting height can be adjusted to the height of the grass.

If the grass is too long for the highest blade setting, use a weed whacker first to trim it down. You can then use your lawnmower on the trimmed grass.

Dirty Blade

Blades that are coated with mud, grass, and other gunk move slowly, and engines work harder to spin them.

Solution

With the engine off and wearing protective gloves, clean the blades to remove all blockages.

Use a brush first, and then a wet cloth to clean the blade of the lawnmower and the lawnmower unit too.

You may use some warm and soapy water to remove persistent dirt and debris from the lawnmower.

Do not forget to clean the deck of the weed eater and the handles.

After cleaning the lawnmower and its parts with water, let it stand for 15-25 minutes to dry off.

Storing the lawnmower while it is wet causes rust and damage to the lawnmower.

Maintenance Is Key

The best way to prevent any type of lawnmower problem is by performing frequent maintenance checks.

If left unresolved, minor issues will lead to extensive damage that will cause your machine to operate at a subpar level.

All lawnmower parts must be cleaned regularly, the correct replacement parts must be used, and they must be stored in cool, dry places.

Lastly, lubricate all the moving parts of the lawnmower. Consult the owner’s manual of your lawnmower for directions on how to carry out lubrication.

The owner’s manual also gives you guidance about the parts that you should lubricate.

Lawnmower Won’t Start? Do this.

Bad gas or a dirty carburetor are the most common reasons for a lawnmower that starts hard or runs rough.

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A lawnmower that won’t start, especially when taken from storage, is almost always due to one problem: bad gas.

Storing a lawnmower in the fall without adding gasoline stabilizer to the fuel tank can cause the fuel to break down and plug the fuel passages. If fixing that problem doesn’t help, there are a few others that can help fix a lawnmower that won’t start, as we explain here.

How to Fix a Lawnmower That Won’t Start

Replace the Bad Gas

Over time (like the six months your lawnmower sat in your garage over the winter), the lighter hydrocarbons in gas can evaporate. This process creates gums and varnish that dirty the carburetor, plug fuel passages and prevent gas from flowing into the combustion chamber.

The carburetor bowl below formed corrosion and deposits during storage, which can easily plug fuel passages and prevent the engine from starting.

Storing equipment without stabilizing the gas can lead to deposits that foul the carburetor or injectors.

Ethanol-containing gas can absorb water from the atmosphere, which can lead to phase separation, which occurs when ethanol and gas separate, much like oil and water. Ethanol that has absorbed enough moisture and has sat long enough can foul the fuel system and prevent the engine from starting.

No matter how many times you yank the pull cord and pollute the air with your advanced vocabulary, the lawnmower won’t start if it’s trying to run on bad gas.

In extreme cases, evaporation of lighter hydrocarbons can change the gasoline’s composition enough to prevent it from igniting. The gas may be fueling the engine, but it doesn’t matter if it won’t ignite.

Bad Gas in Your Lawnmower? Here’s How to Fix It

If you neglected to add gasoline stabilizer to the fuel prior to storage, empty the tank and replace with fresh gas. If the tank is nearly empty, simply topping off with fresh gas is often enough to get it started.

Lawn Mower Will Not Start. You Will Never Guess Why

On some mowers, you can easily remove and empty the fuel tank. Sometimes that’s more trouble than it’s worth. In these cases, use a fluid extraction pump or even a turkey baster to remove the bad gas. You don’t need to remove all of it; but try to get as much out as possible.

Clean the Carburetor

You’ve replaced the fuel, but your lawnmower still won’t start.

Next, try cleaning the carburetor. Remove the air filter and spray carburetor cleaner into the intake. Let it sit for several minutes to help loosen and dissolve varnish and gums.

Remove the air filter and spray carburetor cleaner into the intake. Let it sit a few minutes to loosen deposits.

On some carburetors, you can easily remove the float bowl. If equipped, first remove the small drain plug and drain the gas from the bowl. Remove the float bowl cover and spray the float and narrow fuel passages with carburetor cleaner.

This kind of “quick-and-dirty” carburetor cleaning is usually all it takes to get the gas flowing again and your lawnmower back to cutting grass.

If not, consider removing the carburetor from the engine, disassembling it and giving it a good cleaning. Be forewarned, however: taking apart a carburetor can lead to nothing but frustration for the uninitiated. Take pictures with your phone to aid in reassembly. Note the positions of any linkages or the settings of any mixture screws, if equipped. If you’re at all reluctant, visit the servicing dealer instead.

Consider replacing the carburetor altogether. It’s a fairly simple process on most smaller mowers and it’s often less expensive than taking it to the dealer.

Direct compressed air from the inside of the air filter out to remove debris that may be reducing airflow and preventing the lawnmower from starting.

Clean/Replace the Air Filter

With the air filter removed, now’s the perfect time to clean it.

Tap rigid filters on a workbench or the palm of your hand to dislodge grass clippings, leaves and other debris. Direct compressed air from the inside of the filter out to avoid lodging debris deeper into the media.

Use soap and water to wash foam filters. If it’s been a few years, simply replace the filter; they’re inexpensive and mark the only line of defense against wear-causing debris entering your engine and wearing the cylinder and piston rings.

An incorrectly gapped spark plug can prevent the engine from starting. Set the gap to the specification given in the owner’s manual.

Check the Spark Plug

A dirty or bad spark plug may also be to blame. Remove the plug and inspect condition. A spark plug in a properly running four-stroke engine should last for years and never appear oily or burned. If so, replace it.

Use a spark-plug tester to check for spark. If you don’t have one, clip the spark-plug boot onto the plug, hold the plug against the metal cylinder head and slowly pull the starter cord. You should see a strong, blue spark. It helps to test the plug in a darkened garage. Replace the plug if you don’t see a spark or it appears weak.

While you’re at it, check the spark-plug gap and set it to the factory specifications noted in the lawnmower owner’s manual.

If you know the plug is good, but you still don’t have spark, the coil likely has failed and requires replacement.

Did You Hit a Rock or Other Obstacle?

We’ve all killed a lawnmower engine after hitting a rock or big tree root.

If your lawnmower won’t start in this scenario, you probably sheared the flywheel key. It’s a tiny piece of metal that aligns the flywheel correctly to set the proper engine timing. Hitting an immovable obstacle can immediately stop the mower blade (and crankshaft) while the flywheel keeps spinning, shearing the key.

In this case, the engine timing is off and the mower won’t start until you pull the flywheel and replace the key. It’s an easy enough job IF you have a set of gear pullers lying around the garage. If not, rent a set from a parts store (or buy one…there’s never a bad reason to buy a new tool) or visit the dealer.

My Lawnmower Starts But Runs Poorly

If you finally get the lawnmower started, but it runs like a three-legged dog, try cleaning the carburetor with AMSOIL Power Foam. It’s a potent cleaning agent designed to remove performance-robbing carbon, varnish and other gunk from carburetors and engines.

Add Gasoline Stabilizer to Avoid Most of These Problems

Which sounds better? Completing all these steps each year when your lawnmower won’t start? Or pouring a little gasoline stabilizer into your fuel tank?

Simply using a good gasoline stabilizer can help avoid most of the problems with a lawnmower that won’t start.

AMSOIL Gasoline Stabilizer, for example, keeps fuel fresh up to 12 months. It helps prevent the lighter hydrocarbons from evaporating to reduce gum and varnish and keep the fuel flowing. It also contains corrosion inhibitors for additional protection.

I have a five-gallon gas can in my garage from which I fuel two lawnmowers, two chainsaws, two snowblowers, a string trimmer, an ATV and the occasional brush fire. I treat the fuel with Gasoline Stabilizer every time I fill it so I never have to worry about the gas going bad and causing problems.

You can also use AMSOIL Quickshot. It’s designed primarily to clean carburetors and combustion chambers while addressing problems with ethanol. But it also provides short-term gasoline stabilization of up to six months.

Use a Good Motor Oil for Your Lawnmower

Although motor oil has no bearing on whether your lawnmower starts or not (unless you don’t use oil at all and seize the engine), it pays to use a high-quality motor oil in your lawnmower.

This is especially true for professionals or homeowners running expensive zero-turn or riding mowers.

Lawnmower engines are tougher on oil than most people realize. They’re usually air-cooled, which means they run hotter than liquid-cooled automotive engines.

They often run for hours in hot, dirty, wet conditions. Many don’t have an oil filter, further stressing the oil.

In these conditions, motor oils formulated for standard service can break down, leading to harmful deposits and reduced wear protection.

For maximum performance and life, use a motor oil in your lawnmower designed to deliver commercial-grade protection, like AMSOIL Synthetic Small-Engine Oil.

Its long-life formulation has repeatedly demonstrated its ability to safely exceed original equipment manufacturer (OEM) drain intervals in the toughest conditions. It provides an extra measure of protection when equipment goes longer between oil changes than is recommended by the OEM.

My Lawn Mower Starts Then Dies: What’s Wrong?

Ahhh…the smell of fresh-cut grass. There’s really nothing like it. However, it’s pretty frustrating to be all ready to tackle those tall green blades only to have your mower fire up and then sputter out. If your lawn mower starts then dies, you want a quick answer about what’s to blame, and what to do to fix it. I’ll share the 4 most common causes to this mower problem and what you need to do to address each.

When your mower starts then dies it can feel like you’re alone, but this problem is more common than you might think, and the fix can be an easy one.

Let’s take a look at the four most common reasons behind that false start and how to fix them.

Causes for Lawn Mower Starting then Dying

If your lawn mower starts, runs briefly, then dies these are the four most common reasons that’s happening:

• Dirty carburetor / clogged carburetor bowl
• Old gasoline that has gone bad
• Dirty or defective spark plugs
• Too much oil in your resevoir

Below I’ll get into each potential problem, why it can result in a mower that starts then dies, and what you should do to fix it.

Dirty Carburetor or Clogged Carburetor Bowl

When your lawn mower starts then dies, your carburetor is most likely involved somehow.

Think about it. If you live in a northern region, your mower sits all winter … waiting months without any action.

And, if you live in a more temperate zone, your mower works hard year-around.

In both cases, your carburetor is going to need a little TLC.

What’s so important about the carburetor?

Your engine needs a steady flow of gasoline to run correctly. The carburetor is responsible for mixing gas with just the right amount of oxygen to create combustion.

This combustion supplies a continuous rotation of the crankshaft that is necessary to run the mower’s engine.

If your carburetor is dirty or the carburetor bowl is clogged, the process above is compromised, and your engine may start up, but it will not run properly and may die shortly after you pull the cord.

How do I fix it?

Your dirty carburetor needs a good blowout with an aerosol can of carburetor cleaner. This will cost you less than 10 and will last for a season or two. I use the WD-40 Specialist Fast Acting Carb/Throttle Body Parts Cleaner (Amazon link). This cleaner uses a solvent formula to breakdown carbon contaminants, leaving your carburetor clean and gum-free. I give my mower a shot of that every time a mow, right before pulling the cord, and recommend that you do the same.

The only drawback to this particular cleaner is it does not have a straw for targeted spraying. If you need a more precise application, Gumout makes a cleaner (Amazon link) that will do the trick with its jet spray applicator.

You can purchase either product locally, or online.

Unscrew the carburetor bowl and give it a once over with the cleaner. Be sure to clean the screw and hole with the carburetor cleaner as well. This is where the directional spraying straw is particularly handy. When reattaching the bowl, don’t over-tighten the screw. This could strip the threads enough to distort the seal.

What I Do

For carb maintenance, give a light spray near the air intake hole for your mower’s engine just before you start it up. This is typically just behind the air filter. Remove the filter, give the hole a spray, then replace the filter.

When you start the mower, it’ll be pulled into the engine and clean deposits in your carb.

Old Gasoline in Your Mower

You know your mower can’t run without gasoline, but the quality of the gas is equally important.

If the gas in your mower has been sitting inactive for a while, evaporation has most likely created a damaging residue.

This residue leaves particles that clog your mower’s internal parts.

The end result is restricted gas flow, which means your mower can start and die shortly thereafter. Sometimes, your mower won’t start at all.

How do I fix it?

If your mower tank is less than half full of old gas, you might try adding new gas to dilute the impurities. If the old gas is more than half of a tank, it would be best to siphon it out and fill the tank with fresh gasoline.

In both cases, adding a stabilizer such as Sta-bil Fuel System Stabilizer (Amazon link) is a Smart idea. Stabilizers prevent the clogging residue for up to two years, and at around 10 a bottle, they are an inexpensive additive that can keep your mower running like a champ.

Always read the directions to know the proper fuel to stabilizer ratio for your mower.

What I Do

I used to mix Sta-bil into my fuel, but now I just pay a little extra for 4-cycle TruFuel – an ethanol free gas product that can sit for years without going bad.

It’s more expensive than regular gas mixed with Sta-bil, but a couple of larger cans will get my Honda self-propelled mower (this one from Home Depot if you’re curious) through the mowing season up here in New England, and I like the peace of mind that comes with knowing my mower and snow blower always start on the first pull, and I don’t have to worry about bad gas giving me problems when I’m ready to mow or need to clear the driveway.

You can buy it online, or locally at Home Depot or some local hardware stores.

Dirty or Defective Spark Plugs

Spark plugs supply the “spark” that ignites the air/fuel mixture in your engine.

This small explosion makes your engine produce power.

The spark plugs are an essential component of your mower’s ignition system. If they are dirty or faulty, they will not spark, and your mower will not start, or may start and then quickly die.

How do I fix it?

Your mower’s spark plug(s) are easy to find. In most walk-behind mowers they’re covered with a black cable and right in the front of your mower.

You’ll need a socket wrench of the right size to remove your plug (check your manual to find the correct size for your mower/spark plug).

If your spark plugs are not too heavily coated with build-up, you can try cleaning them. You should never clean a spark plug with a shot-blasting cleaner. A wire brush and appropriate cleaner will do the trick if the plug is just dirty.

However, if your mower’s spark plug looks filthy or appears to have a dark carbon residue, you might be better off replacing.

This is an easy job and it’s inexpensive – a new spark plug with be 8-9 and your size is probably available locally.

What I Do

Spark plugs should be replaced every year or two for problem-free mowing, and I do mine annually as part of my spring mower maintenance.

I get a new air filter and change the oil in my mower at the same time. This runs me about 20 total, takes me about 15 minutes, and keeps my mower in perfect working condition.

Replacing Your Spark Plug

Removing your spark plug is an easy job anyone can do. Simply unhook the spark plug wire and remove the old plug with a spark plug socket.

Replacing a spark plug can be a bit more challenging for a first-timer, but I still consider it an easy job.

Use a spark plug gauge to measure the gap between the two electrodes at the tip of your spark plug. Check for the specifications for your model to know the recommended size of the gap.

If necessary, use a spark plug gauge to adjust the gap by gently bending the curved electrode. When the gap is correct, the gauge will drag a bit as you pull it through the gap.

Now you can install the new plug and attach the spark plug lead. Be careful not to over-tighten on installation.

If you have never done this before, there are several videos online that can be of great assistance, but my advice is that as soon as it starts to feel snug, give it no more than another quarter turn to prevent damage.

Too Much Oil in the Mower’s Reservoir

If your carburetor is clean and the spark plugs are firing, the problem might be too much oil.

I believe it’s human nature to want to over-fill a lawn mower’s oil reservoir, especially if you’re not particularly handy. You feel so accomplished that we’re doing the job yourself that you go overboard and over-fill the tank.

It happens, and it’s not the end of the world (or your mower).

White smoke coming out of the engine is a tell-tale sign that excessive oil is the culprit.

If a lot of smoke is coming out, your mower might be running, but not for long. In this case, the excess oil will eventually drown out the engine and cause it to die.

How do I fix it?

This is actually an easy fix. If you have too much oil, you just need to drain some. You can use a siphon, or (if you have a walk-behind mower) you can tip your mower and drain the oil from the hole where you add it.

What I Do

I’m guilty of overfilling the oil tank sometimes too, so I’ve learned to go slow when I add oil. I check, and check again with the dipstick and gradually bring the level up to the proper place.

If you have overfilled your oil tank, I advise that you use a dipstick to measure the amount of oil in the reservoir before removing it, and then again after to make sure you get the right level.

Not enough oil is another (and more serious) problem, and you would not want to inadvertently trade one issue for another.

After draining some oil and checking to see if you have an adequate amount, start the mower again.

If the mower fires and stays running without the billowing puffs of white smoke, you have corrected your problem.

Lawn Mower Starts Then Dies: When it’s Time to Call a Professional

If you have tested all of the methods I’ve shared for fixing your lawn mower that starts and then dies, hopefully your problem is solved.

But if not, it might be time to throw in the shop towel and call a professional.

The following are other issues that could be keeping your mower from running properly.

Serious Reasons Your Lawn Mower Starts Then Dies

• Worn out carburetor: If your carburetor is more than dirty, it might be time to replace it.
• Faulty choke: Unless you are extremely handy, identifying this problem and restoring the delicate balance necessary to get your engine purring like a kitten is another issue for the experts.
• Gas tank or gas line blockage: Anytime your gasoline is not getting to the engine, your mower will not run properly. A blockage of any kind that prevents the constant flow of gas is a problem that might take a trained eye to identify and fix.

The average weekend warrior with limited knowledge on the matter will probably feel more comfortable hiring someone with the experience and the tools to get the job done right.

I recommend that you start by checking your mower’s warranty. If it’s covered, a repair may not cost you anything. Some companies will send someone right to your home, or come to pick up your mower to save you time.

If your mower isn’t covered by warranty, find a local small-engine repair shop that has good reviews. These guys can fix almost anything, and their are typically lower than you’d expect.

Preventing Mower Problems

The best way to ensure your mower will fire up and run like a champ is to put preventative measures in place.

I have tips for winterizing your mower, and a spring maintenance checklist that you can check out if you’d like to learn more.

To summarize those here, however:

• Clean your air filter regularly (replace it annually).
• Change your spark plugs every 1-2 years.
• Keep stored oil and gasoline clean. Use a stabilizer in your gas to keep it fresh for up to two years, or pay extra for 4-cycle TruFuel.
• Keep your engine clean with an engine degreaser.
• Use the dipstick and don’t overfill your oil reservoir.
• Keep your carburetor clean with a carburetor cleaner spray.

Performing regular maintenance on your mower is the best way to keep it running smoothly, and investing a few bucks per year in this is worth it.

You’ll avoid headaches, repair costs, and your mower will last a long time, starting right up when you need it.

If you do encounter a problem with your lawn mower, decide if you are comfortable with trying to fix it yourself.

If the issue seems to be something beyond the basics, don’t hesitate to call a professional. There’s no shame in this, and sometimes do-it-yourself repairs are just not worth the time, energy, or frustration.

But if you are up for the challenge of fixing the problem yourself, the above guidelines provide a good starting place, and online videos may also be useful. I think YouTube is a great resource.

The main thing is that you get your mower fixed so you can get out there and make your lawn the envy of the neighborhood.

What to do if your lawn mower won’t start

We’ve got all the advice about what to do if your lawn mower won’t start.

A perfectly mown lawn is a great asset to your yard but what do you do if your lawn mower won’t start? We’ll take you through some of the most common mower problems and tell you how to fix them.

Even if you’ve got one of the best gas lawn mowers, sometimes these trusty tools give up on us which is why we’ll show you how to spot problems, the most common reasons a mower won’t start, and what to do about it. We’ll also give you tips on how to fix the best riding lawn mower.

It’s well worth noting, however, that before starting any repairs, make sure your mower is unplugged or switched off with the brake engaged. Disconnect the spark plug cable and don’t repair it near naked flames. Make sure to always service the machine on a flat surface in a well-ventilated shed or garage with the doors open, or better still, go outdoors. Wear safety gloves and goggles, and dispose of used oil considerately at an auto shop or your city dump.

Usually, problems with starting your lawn mower will happen after it has been put away for winter.

Leaving your machine for weeks without use can cause moving parts to gum up. Valves, filters, and seals can become clogged with dirt and dust. It’s best to give your machine a service at the beginning of the new mowing season and we’ll be running through exactly how to do that.

How to start a lawn mower after winter

When you first bring your mower out of the shed or garage in the spring, give it a good once-over before attempting to start it. Clean your machine, especially places where cut grass can accumulate. Oil moving parts and check that cables are problem-free. You may need to change the oil and gas (we tell you how to do this below). Once satisfied that your machine is clean, lubricated, and well maintained, you can turn it on.

What causes a lawn mower not to start?

If you’ve followed the advice above and your machine still won’t start, there are several problems that might be happening.

For all types of mower, a blockage to the blades may stop the machine from working. To tackle this, check the cutting deck to make sure it’s clear and clean, remove any string, branches or vegetation, and check no blades are broken.

If you have one of the best gas lawn mowers, you need the combination of fuel plus a spark to start the engine. The spark comes from a spark plug with an ignition provided by a pull-cord or key. If the cord is stuck or difficult to pull, it can be impossible to get it to spark well enough to ignite the gas. If there’s a problem with the spark plug, ignition, or cables, that can also cause the machine to fail to start.

For even the best electric mowers, you need a good power source, which might be a cable and plug, or a rechargeable battery. Problems can be due to a break in the cable, a loose connection, or a problem with the starting lever. Problems with rechargeable machines may be due to the battery not charging properly.

Robot machines can face problems with charging, connectivity and obstacles. They can also come into difficulty with hilly lawns.

How to fix a lawn mower that won’t start

For gas and ride-on mowers:

• Check the oil level before starting the machine and see that it is clear, not dark and full of debris; if it is, you should change the oil.
• Replace the old gas. Empty the gas from your machine (follow your manual instructions) and replace it with new fuel. For more on this, head to our feature on how to change lawn mower oil.
• Next, change the air filter, which may be clogged with dust and debris. If your machine starts up but stops when you have been mowing a while, a clogged air filter is often the culprit.
• The carburetor can get clogged with debris from fuel that has been sitting in the machine. Remove and soak in a carb-cleaner (vinegar also works) or replace if necessary.
• A faulty sparkplug can cause problems, so remove it and check for discoloration or corrosion. You may be able to clean and replace it but it’s often best to install a new one. Check the cable to ensure it provides a good current. Take extra care with this step.
• With the brake engaged, check for slackness in the brake cable and tighten, following your machine’s manual.
• If gas isn’t getting to the engine, see if you can spot a broken or clogged fuel pipe and replace it necessary.
• Check to see if there is something impeding the pull-cord and free it if need be.

For electric mowers:

• Check the cable is not broken and that it’s attached to the machine and the plug. If it’s damaged, or you have accidentally cut through it, you can replace it. Check your instructions for how to do this.
• Check for something blocking the starter switch – the cord may slip behind it, so make sure you fix it out of the way. If the switch fails, you can replace it, though it’s more tricky than replacing a cable, so make sure you read up.
• Clear the air vents of leaves and dust.
• Rechargeable batteries may come to the end of their life and need replacing, though most should last 2,000 charges. Fully charge the battery, then let it run down completely before charging again.

How do I know if my lawn mower spark plug is bad?

Spark plugs wear out and the most common symptoms of a bad sparkplug include failure to start, the machine being harder to start, poor performance, and using excess fuel. Remove the plug to check for discoloration or corrosion and replace it with a fresh one.

Can old gas cause a lawn mower not to start?

Gas deteriorates over time too. Sediments form and octane-boosters evaporate, making gas less combustible. Siphon the gas out, following the maker’s instructions, clean or replace the carburetor and fill with fresh gas.

Two-stroke or four-stroke problems; what’s the difference?

Problems and their solutions can be different depending on whether your machine has a two-stroke or a four-stroke engine.

A two-stroke engine is usually found on lawn mowers or chainsaws. Because their moving parts are not in a separate, oil-filled chamber, they can wear out faster than those in four-stroke engines. They use a lot of oil too, which can become expensive and they suffer from greater wear and tear and give off higher emissions than a four-stroke engine. However, they are lighter, simpler machines and therefore easier to use and to repair yourself.

If you have a large lawn, you might choose a four-stroke, riding lawn mower, that has a sealed engine, lubricated compartment allowing moving parts to run much longer before wearing out; it has fewer emissions too. They’re more complex machines and you’re best advised to have them serviced and fixed by your dealership, though some maintenance and quick fixes can still be done by you if you’re handy.