How to Troubleshoot and Fix a Lawn Mower That Won’t Start After Sitting

Your lawnmower is the key piece of equipment that keeps your yard looking neat and clean all throughout the summer.

A long winter in storage, or failing to put away your lawnmower without some basic maintenance can make it difficult to start.

Even a well-maintained mower can still run into problems during the peak season. So, what do you do when your lawnmower won’t start?

Of course, there’s no one size fits all answer to a lawnmower that won’t start. The following is a list of possible options to help you troubleshoot and fix a lawn mower that won’t start.

Why My Lawn Mower Won’t Start After Sitting – Here’s How To Fixed It

Sometimes it’s the littlest things that cause big problems. Checking some of the common little foibles is a good place to start, before digging into more major questions like the carburetor or bad spark plug.

Follow the throttle control cable down from the handle to make sure it isn’t getting compressed somewhere along the line.

If you like to collapse or fold your lawn mower handle when not in use, the throttle cable could have gotten pinched in one of the handle joints.

When this happens it can impede its the ability to affect the throttle or choke.

While you are at it, carefully check the underside of the mower deck.

If you have a bad habit of forgetting to clean out old grass clippings and gunk from the mower deck, it could cause the blades to bog down, which in severe cases can bog the motor down so much that it quits.

The gas cap also deserves a good hard look. Most push mowers have some type of breather hole in the gas cap.

This allows a small amount of air to replace the gasoline being taken into the system. If one or all of those holes are plugged by grass clippings or other debris it can hamper gas entering the system.

During the course of your look through, check for loose bolts, rusted or jammed springs or things that have tightened up due to rust.

Sometimes a little corrosion on the throttle control can cause it to stick in place. A little spray with a penetrating lubricant like WD40 can help loosen things up.

Is It A Problem With The Fuel?

What Kind Of Oil Should I Use In My Lawn Mower_

Lawnmower engines are inherently simple, especially compared to the sophisticated engine in your car.

Don’t let this tempt you into thinking that the mower’s engine is crude or invulnerable. Fuel quality matters. Especially if you are taking the lawnmower out for the first time in the year.

Gasoline has a nasty habit of degrading over time. Gasoline in the United States that has a trace amount of ethanol in it is also prone to separating which leaves a small amount of water in the fuel tank.

If your lawnmower has been in the garage all winter, chances are there is a little water in the tank.

Ideally, when you put it away at the end of each summer, you should put some fuel stabilizer in the tank. This will help prevent fuel degradation and water separation.

If you didn’t put fuel stabilizer in it, then you should consider treating the old gas in the tank with some Iso-Heat or a similar product. Then top up the tank with some fresh high-octane gasoline.

What Kind Of Oil Should I Use In My Lawn Mower?

Did I Mix The 2-Cycle Oil Wrong?

These days newer lawnmowers come with four-stroke engines, that need periodic oil changes just like a car.

Yet there are some older lawnmowers out there, and a few new lawnmower manufacturers who still run on a two-stroke engine.

Two-stroke engines typically need to have the fuel mixed with a small amount of special two-cycle oil.

It’s worth bearing in mind that two-cycle oil is a little bit different from the SAE 10W 30 that you put in your car. 

Make sure to double-check the owner’s manual for the type of two-cycle oil recommended by the manufacturer.

If you don’t have the manual anymore, your best bet is to use a two-cycle oil that is rated for “Air-Cooled Engines.”

Now even if you have the right oil in hand, you don’t just dump some into the tank. It needs to be mixed to the proper ratio with fresh gas. If you have old gas in the tank it’s best to siphon it out and start anew.

It’s best to mix the oil and fuel in a separate gas can. Most 2-cycle lawnmowers will tell you the proper mix ratio on the top or it will be stamped on the fuel tank.

Pour the specified amount of two-cycle oil into the empty gas can. Then add one gallon of fresh, high octane gasoline.

Seal the can and gives it a modest swish to make sure the oil and gasoline are thoroughly blended.

Is My Lawn Mower Battery Dead?

How to Know When a Lawn Mower Battery Is Dead

Most push mowers have a pull cord or an electric starting assistant. However, most riding lawnmowers have a small 12 Volt battery that provides the initial spark.

Just like the battery in your car, it can get older, suffer from corrosion and internal components can degrade.

This can impede its ability to hold a charge, to the point where it simply can’t turn the motor over enough to get it started.

If you live in an area where winter temperatures dip below freezing the fluid inside an older battery can freeze.

Sometimes the problem can be so severe that it even damages the battery. If you didn’t take it out and store it indoors at the end of the last summer, the battery may be out of charge or dead.

Sometimes a dead battery will cause the motor to make a clicking sound when you turn the key. A totally flat battery might not even make a sound!

How To Fix A Battery That Will Not Charge

At the start of every season, you should put the battery on a smart charger the night before.

Set it for trickle charge, this will slowly charge the battery up to its maximum possible level. In the case of a damaged or degraded battery, this level might still be too low to turn the motor over.

If you’ve tried charging it for several hours and it still won’t go, chances are you need to totally replace the battery.

You can write down all the information on the battery tag, or simply take a picture of it on your phone.

Most box hardware stores carry replacement mower batteries that already have a significant amount of charge.

Is It The Air Filter?

Remove Air Filter Then Clean It

Another thing to check while you are poking around the mower is the air filter. If it’s clogged with dust, pollen, or other debris it won’t let enough air through to the spark plug.

Sometimes a simple air filter cleaning is just the ticket for getting a stubborn lawnmower to start.

There are different types of filters. Newer mowers might have a replacement filter for sale.

Older mowers and mowers with small engines sometimes have a simple foam air filter which can clog up. A meticulous hand cleaning can usually get it cleared up again.

You should never try to soak an air filter in gasoline, ether, or starting fluid in hopes of getting the lawnmower to turn over.

This old fashioned air filter “Hack” might work once or twice, but it is very dangerous and could cause a very serious fire!

Is It A Problem With The Carburetor?

How To Clean A Carburetor On A Lawn Mower Without Removing It

Most push mowers use a carbureted engine, where air and fuel mix. Any time a carburetor is left to sit too long unused it can be at risk for gumming up.

As time goes on residue and other tiny pieces of debris can gradually start to build up inside the carburetor.

An air filter that has gone too long without cleaning can also contribute to carburetor debris.

As residue and other unwanted materials build-up, it can make it increasingly hard to start the lawnmower.

In a severe case, the pull cord might wear your arm out before the mower even hints at starting.

There is a way to check if it is indeed the carburetor at fault.

If there’s gas in the tank, the fuel valve is on, and you feel confident that the spark plug is still good, you can try spraying a one-second burst of carburetor cleaner or aerosol lubricant straight down the throat of the carburetor.

Then quickly engage the handle control and give the pull cord you best yank. If the engine sputters and struggles, then dies, it is likely a fuel problem.

If you pull the cord in earnest for three or four times and it still sits there, stone dead and mocking you, then chances are something more serious. Most likely the carburetor or spark plug.

If you shine a flashlight down the throat into the carburetor and you see a fair amount of corrosion, chances are there’s no bringing it back to life.

You would be better replacing it yourself, or if you aren’t all that handy, call around to get some quotes for a carb replacement from local lawnmower repair shops.

Checking The Fuel line

Look At The Connecting Wires In The Carburetor

If the engine fired up then died, you might want to check the fuel line. If you gently disconnect it below the carb and a little fuel leaks out, you can rule out a fuel line problem.

If, however, the fuel line is looking relatively dry, then it’s likely a fuel line problem. In many of these cases, it turns out to be an old or clogged fuel filter that needs to be replaced.

Why Should You Change the Fuel Filter?

Just like how the air filter helps prevent airborne contaminants like pollen and dust from reaching the carburetor, the lawnmower’s fuel filter helps prevent debris and contaminants from passing through the fuel line.

When gasoline sits for too long in the gas tank, it can develop gummy tarnished debris which can move through the fuel line to clog the fuel filter.

This is even more likely to be a problem if you have grass clippings or other debris happen to fall into the fuel tank when you refill during a long cutting session.

Where is My Fuel Filter Located?

How Do I Replace My Lawnmower’s Fuel Filter

Most of the time the fuel filters are located either inside the fuel tank or it is attached directly to the fuel line in between the fuel pump and the tank.

There are a few manufacturers who produce mower engines have an internal, fuel filter, which is simply not serviceable without professional help.

If your fuel filter is one that can be accessed easily and you have a modest amount of mechanical sympathy, you might just be able to replace it yourself.

The first step in this somewhat complicated process is making sure you can find the right replacement filter.

A quick flip through the owner’s manual is certainly called for. If you don’t have the manual, you might be able to look up the part number for your particular model online.

With the correct information in hand, call up the local auto parts store, or anywhere that sells replacement lawnmower parts.

They might have it currently in-stock or they can special order it for you. In the case of a special order, double-check the manufacturer or another online vendor’s pricing.

With free shipping deals becoming more and more popular, you might be able to order it for yourself for less than what the parts store is offering!

It’s not always the case, but you might just be able to save yourself a couple of bucks along the way.

Safety First!

How Do I Drain And Change The Lawnmower Oil_

Replacing a fuel filter is exactly the sort of thing that protective eyewear was invented for. The filter and fuel line itself has a nasty habit of accidentally spraying a little gasoline in your eyes.

Even the fuel vapors themselves can start to cause severe irritation of the cornea. Believe me, gasoline in your eye is a whole new threshold of suffering that will derail the project and possibly the rest of your day.

Before you get started it’s also a good idea to have a dry cloth handy or some clean shop rags.

I personally like to set aside an old plastic container, like the cut off the bottom of a milk jug, just to hold the filter and clean up any little fuel drips.

In a situation where the filter is inside the tank, yet easily accessible, you need to thoroughly drain the gas tank to get at it.

How Do I Replace My Lawnmower’s Fuel Filter?

It is usually located near the base of the fuel tank, by the gas line. If your tank doesn’t have a fuel valve, you will have to clamp the gas line.

There are hardware stores and auto parts stores who sell a special fuel line clamp. It works perfectly.

Unfortunately, it’s what’s called a “Uni-Tasker.” If you aren’t the kind of person who is frequently tooling around with small engines, you might use this thing two or three times a decade.

Chances are you’ll lose it after a year and need to buy a new one!

If you are a fisherman, or there is a bait and tackle shop relatively nearby, you can make do with a cheap surgical clamp. It’s meant to help firmly grasp a hook in a fish’s mouth.

However, if your mower is a little old, or the fuel line looks a bit on the brittle side, this is not the best option, as it could damage the fuel line. So, embrace this “Hack” with caution!

For a fuel filter that is connected to the fuel line, you will need to carefully remove the metal clips on each side of the filter.

Needle-Nose pliers are typically the tool of choice for doing this, but you might also need the help of a flathead screwdriver. Once it is loose from the clips you should be able to slide the filter off of the fuel line.

Give the filter a little shake, and then use a clean shop rag to wipe out any lingering fuel. If there is stuck on residue or varnish it might take a little extra elbow grease with a second clean rag.  

The bottom side of the filter housing should have a mesh screen. When it’s properly clean you should be able to see light passing through it.

If you can’t then there is likely still residue in the mesh. Pouring a small amount of fresh gasoline through the mesh might be all it needs to clear.

At that point, you can remove the old filter. Then carefully insert the new filter. When you reinstall the filter, make sure that the metal clips on both sides of the filter are securely reconnected.  

Once this is done you can carefully release the clamp on the fuel line. Then look everything over to check for any obvious leaks.

If your lawnmower has a primer bulb, you can give it two or three pumps to run fresh fuel through the filter and fuel line. If you do find a leak, you will need to address it before using the lawnmower again.

Is It A Problem With The Spark Plug?

What Are Some Signs Of A Bad Spark Plug

The spark plug is the first thing to check. A dirty or loose connection can impede the spark, which is necessary for the engine to run.

At the same time, a faulty spark plug can also lead to problems with the motor flooding with too much gas.

When this happens there is simply too much fuel for the air to ignite, and the mower sputters or doesn’t turn over at all.

Sometimes a clogged carburetor is the primary cause or is contributing to the spark plug’s inability to ignite the fuel and air mixture in the combustion chamber.

To tell if this is a factor, you should carefully remove the bad spark plug. 

In the case of a riding lawnmower, the battery could also be a factor. If the battery lacks sufficient charge to start the motor, it will simply sit there.

Perhaps you’ll hear a little click, or it might even spin the starter slowly with a sort of slowly wheezing groan.

In a case like this, you can connect the battery to a charger for an hour or two and it should have enough charge to fire up.

If it still doesn’t then chances are either the battery itself has died, or there is a loose connection. Double-check the battery’s ground wire for any rust or corrosion.

What do you do when your lawn mower starts smoking?

What do you do when your lawn mower starts smoking?

Gas-powered lawnmowers can smoke from time to time. The type of smoke they produce can sometimes help you diagnose an underlying problem.

This can go a long way toward figuring out what you need to repair, replace, or simply adjust.

White or blue-tinged smoke is usually a sign that the lawnmower is burning oil.

If it’s a stroke-lawnmower, a little bit of smoke at startup is nothing to worry about. If it persists, then it likely means that you mixed the oil and fuel a little too rich.

This essentially means there is excess 2-cycle oil in the gas tank. Adding a tiny amount of straight, high octane gasoline, may help resolve the problem.

When in doubt, you can empty the tank and refill it with properly mixed fuel.

If you are certain that the fuel to oil was properly mixed, or you have a 4-stroke engine, persistent smoke could be a sign of a more significant malfunction.

Usually, this is a sign of a failing seal or gasket that is allowing the oil to enter the combustion chamber.

If you aren’t mechanically adept, you will likely need to take the lawnmower to a certified mechanic.

Black smoke is often the sign of a clogged air filter that is altering the fuel to air ratio. Taking out the air filter and giving it a thorough cleaning will usually help clear this up.

How to Prevent Your Lawnmower From Not Starting After Winter Storage

You shouldn’t let a lawnmower’s basic nature lure you into thinking it’s invulnerable. The truth is, it needs much of the same basic maintenance that your care does!

Putting fuel stabilizer in the gas tank and always using fresh gas will go a long way toward preventing carburetor and fuel filter problems.

Changing the oil periodically or making sure to mix two-cycle oil in the proper ratio helps prevent smoking and makes sure that the moving parts in your lawnmower’s engine are moving the correct way.

Keeping an eye on the air filter, and occasionally peaking at the carburetor helps make sure that the lawnmower’s engine is getting the air it needs to fire properly.

A seasonal inspection of the spark plug will also go a long way toward catching a bad plug before it leads to even more complications.

You also might need to sharpen the mower’s blades and clean the underside of the mower deck to ensure that it doesn’t bog down or stall when you need to cut a path of tall grass.

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