So your lawn mower has been stored in the shed or garage all winter long. Now you’re having trouble getting it started and you’re wondering how to start a lawn mower that has been sitting.
Or maybe you found or inherited a lawn mower second hand that hasn’t been used in years.
Well, you’ve come to the right place. Here’s your introductory guide to lawn mowers and how to start a lawn mower that has been sitting!
First and foremost, proper safety measures are important when working with a lawn mower. Remember to use some safety gloves, safety glasses, and to be aware of the sharp blade and engine parts.
Use this article as your guide. You can also find how-to videos on Youtube specifically for your brand or model of mower
This article will provide you with the information you need to get your mower started.
It should help regardless of what type of lawn mower you own.
Let’s get started.
Check & Change the Oil
For a mower that has been sitting for quite a while, it’s definitely a good idea to check the oil. The best time to change the oil in your mower is about an hour after you finish mowing. But if it has been sitting all winter, check the oil before you even try to start it.
First, check that the oil is good quality, doesn’t have residue in it, and that there is enough of it.
If the oil is very dark or black, it’s time to change the oil so your mower runs smoothly and lasts a long time.
I change the oil in my mower twice a year – once at the beginning of the season, and once just before I put it away for the winter.
If you haven’t done it recently, just give the lawn mower an oil change. Even if this isn’t the primary issue that’s preventing your mower from starting, it’s probably a contributing factor.
Mowers are small engines that don’t require a lot of oil at all. This makes it a pretty inexpensive tune-up to do yourself at home. With a walk-behind mower you’re looking at 10 minutes or less.
Disposing of Your Lawn Mower Oil
Be sure to collect the oil in an appropriate container (I use an empty Gatorade bottle). You want something that caps tight and that won’t spill. I bring it to my local auto shop for disposal.
Your local mechanic or oil change shop will usually take your used motor oil. But if not, there may be disposal programs at your city dump.
If smoke is coming from the mower, that’s another sign that the oil needs to be checked and changed.
A mower that won’t start obviously is not going to smoke. Still, it’s worth mentioning as something worth watching for so you can stay on top of mower maintenance.
A smoking mower could indicate that there is an oil leak somewhere. The leak causes the oil to burn as it comes into contact with hot metal.
It could also indicate that there is not enough oil, which can permanently damage your engine.
Check the Gas Tank, Genius
Have you ever called tech support and the first thing they ask you is if your computer/TV is plugged in?
Same goes for your lawn mower.
Make sure you have gas in the tank!
Gasoline isn’t very stable. If the gas in your mower is more than 30 days old, you’ll need to empty the tank. You may be able to dump the tank by tipping the mower. If not, you will need to siphon it.
After you’re done, put fresh gas into the mower.
The exception to this fix would be if you personally put fuel stabilizer into the gas tank before storing it.
My Recommendation for No-Hassle Gas
Personally I use a product called TruFuel (you can get it at your local box store and most hardware stores carry it). This product is pure, “old school” gasoline without any ethanol added.
You don’t have to add fuel stabilizer, it runs clean, and it can sit in your mower all winter and your mower will start up first pull. I use it in my mower and snowblower and it’s awesome.
It’s expensive compared to regular gas, but it’s cheaper than replacing your mower or buying a new carburetor every few years.
And I’m the Lawn Chick! My mower deserves the best. 🙂
If you do have to siphon out old gas and replace it, remember that mowers take the same gasoline that goes into your car. Rather than trying to dispose of it, you can usually just top off your car’s gas tank. Just make sure that it’s not contaminated gas – if that’s the case then make sure to dispose of it properly according to your municipal guidelines.
Change the Air Filter (it’s easy)
After checking the gas tank and changing the oil, check the air filter on your mower. These can get clogged.
Oxygen is a vital component for combustion in an engine. If your mower’s air filter is dirty your mower won’t run well (or at all).
It is best to replace a clogged filter as opposed to trying to clean it. Even a small perforation in the filter can let in dust or residue that will ruin your engine.
A particularly telling sign of a clogged air filter is if your mower starts but then stops while you are mowing the lawn.
Also, you can look at it. If it’s dirty, you’ll be able to tell because, well, it will look dirty.
Where to Get an Air Filter for Your Mower
Most box stores near you will probably carry the right size air filter for your mower. You can expect to pay around $10 for a new one.
I recommend replacing your air filter annually as part of your regular maintenance.
If you can find the air filter on your mower, then you can replace it. Don’t be intimidated. Replacing the air filter is as simple as removing the old one and placing the new one in its place).
A clogged air filter may not be your only issue. But it’s a good idea to replace your filter when you’re fixing up a lawn mower that won’t start.
Replace Your Mower’s Spark Plug
You will find your mower’s spark plug at the front end of the mower (especially with a walk-behind mower). It is easy to locate because it has a wire that attaches to it. This is usually black rubber and covers the spark plug to keep dirt and debris out.
Make sure that the wire is in good shape and that there is a good connection there.
The next thing to check is the spark plug itself.
You can remove your mower’s spark plug using a socket wrench. You may need to experiment to find the right size. Or you can look it up online. The old spark plug should come out with a few simple twists.
When you remove the spark plug it will be obvious if you need a new one. Look for corrosion or discoloration at the business end of the spark plug. That’s the end that was in the mower (the one with the threads and the small metal piece sticking out). There should not be any corrosion on it.
You can try to clean it up and reconnect it to see if it will work. But, when in doubt just replace the spark plug.
How to Replace a Lawn Mower Spark Plug
Like the air filter, this is not a complicated job. You just need to find the correct socket wrench for your plug and be careful not to over-tighten it when installing the new one.
My advice is to replace your spark plug, even if your spark plug looks relatively new. I replace mine every other year.
In my experience if your mower isn’t starting up after sitting over the winter and you’ve checked the oil and replaced the gas, it’s usually a problem with your spark plug. Parts can often be found at your local hardware store or on Amazon, and a new spark plug is only a few dollars.
Speaking of spark plugs. This is a good time to remind you that it’s always best to disconnect the spark plug if you decide to troubleshoot anything with the lawn mower’s engine.
This is a safety measure to ensure that the engine doesn’t start while you’re working on it. Just unplug the black wire/cable that runs to and covers the end of the spark plug.
Tighten the Mower’s Brake Cable
If the brake cable is loose on your lawn mower, then the mower may not start. To check the tension on the brake, pull the brake handle and then use your hand to pull on the brake cable to see if it is properly tense or if there is any give.
One trick to check to see if this might be your problem is to try starting the mower while you old the brake cable tight. If the mower starts then you’ll know your brake cable needs tightening.
This is usually an easy job. You can complete it quickly with a crescent wrench and a set of vice grips.
What a Dirty, Dirty Carburetor
Issues with the carburetor (or the carb, as it is affectionately known in the biz) are an incredibly common reason for a faulty mower.
After you check the gas, oil, filter, and spark plug, a dirty carburetor is probably the culprit if your mower still won’t start after sitting a long time.
Often, you’ll find that the carb is corroded or that it has clogged if fuel was left in the engine and left to evaporate leaving behind a sticky residue inside the mower’s carburetor.
It’s possible to try cleaning the carb by giving it a good, long soak in a carb cleaner or in vinegar.
If this doesn’t work, carburetors for lawn mowers are not incredibly expensive and they are also relatively easy to find online.
Can I Do This Myself?
Of all the repairs you can tackle, this is the one that people get most intimidated about, but if you’re handy, you can probably find and follow a YouTube video for your model mower that will show you the steps involved.
Are there Other Options?
One work-around if you don’t have the time right away to take your lawn mower engine apart to clean out the carb is to use some starting fluid spray.
A can will just cost a few bucks, and you spray it into the engine right behind where the air filter is (don’t spray it on the air filter). This will typically get your mower running until you have time to get it properly serviced.
Replace Your Fuel Pump?
The fuel pump does exactly what it sounds like … it pumps fuel from the gas tank into the engine via a series of three ports.
If there is too much oil in the engine, then the oil can leak into the fuel pump (specifically into the pulse port line) and make your mower’s fuel pump defective.
To see if the fuel pump isn’t working anymore, check the pulse port line, valves, and the diaphragm inside the pump.
If you’ve tried most of the other potential problems in this article and your mower still won’t start, replace your fuel pump.
Unfortunately it is not possible to repair the fuel pump, it must be replaced. It’s a lot cheaper than buying a new mower, though.
Check For a Broken Flywheel Key
The flywheel is the big horizontal spinning wheel in the mower.
This is the part that begins spinning when you pull the starter cord on your walk-behind mower.
Sometimes hitting a hard object with the mower can break the flywheel key, which prevents the mower from starting when you pull the cord.
While this probably isn’t the issue if you’re wondering how to start a lawn mower that has been sitting over the winter … if you hit a root, rock, or a large felled tree branch on your last mow of the season then this could be the culprit. So I thought it was worth mentioning.
To check the flywheel key, you will need to remove the flywheel on your mower.
Removing the flywheel is a tedious process because the nut keeping it on is very tight and the flywheel needs to remain stationary in order to loosen the nut.
What Not To Do When Replacing This Part
Most guys and gals trying to DIY this will stick a broomhandle or some tool between the blades of the wheel, but this is a bad idea. This can easily break the blades, which are expensive to replace.
I recommend that you use a clamp – which is secure and safe.
To find a method that will work with your mower, find a YouTube video. If your mower’s flywheel key is indeed broken, then you can replace it in less than an hour once you have the new flywheel key.
The fins of the flywheel itself can also get clogged with grass or clippings – this is easy to determine just by uncovering the flywheel itself. If there is any debris, use a clean paint brush to brush it away.
Don’t Give Up On Your Lawn Mower, it’s Probably Worth Saving
I cannot tell you how many people give up on a 3-year old mower that won’t start after the winter, sending it along to the land fill and shelling out big bucks for a brand new model.
There are exceptions, but most of the time a lawn mower that won’t start after sitting is not defective, it has just lacked proper maintenance.
Don’t give up on that old mower just yet!
Troubleshooting most lawn mowers can effectively get them working again, and usually once you do resolve the issue with your mower successfully, you’ll be so much more knowledgeable about maintaining them that you won’t have any problems again.
Cost effective repairs are easy to do at home in your own garage, even if it’s your first time doing them. You can find the parts you need at the hardware store or online.
Not only does repairing your mower save it from the landfill, but it saves you money and can bring you great satisfaction.
However, if all else fails and you do end up needing a new mower, see if your old mower could be useful for spare parts before taking it to the dump. There are probably plenty of small engine repair shops nearby that would be happy to pay a few bucks for it, or take it off your hands for free.
At Lawn Chick, I am committed to publishing accurate, useful, and trustworthy resources for my readers. As part of this commitment, I’ve invited subject matter experts to review our articles for accuracy. I invite you to read our editorial policy and publishing standards which outlines in detail how every article on this site is sourced, edited, fact-checked, and vetted.