There are a number of reasons, mechanical and otherwise, why a mower won’t run. The good news is that fixing most all of the issues is easy enough for a DIYer to handle.
By Tony Carrick and Manasa Reddigari | Updated Aug 8, 2022 4:03 PM
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Lawn care can be tedious, but once the grass starts growing in the spring, mowing becomes a fact of life in most neighborhoods. When you finally muster the strength to tackle that first cut of the season, there are few sounds as disheartening as that of a lawn mower engine that turns over but doesn’t start.
Before you drag the mower in for repairs or invest in costly replacement parts, first make sure that a clogged air filter, soiled spark plug, damaged safety cable, clogged mowing deck, or contaminated gas isn’t to blame. Work through the following steps, and you may be able to get your puttering grass guzzler up and running again in no time.
A lawn mower repair professional can help. Get free, no-commitment repair estimates from pros near you.
Change the lawn mower carburetor filter.
Your lawn mower’s air filter guards the carburetor and engine from debris like grass clippings and dirt. When the air filter becomes clogged or too dirty, it can prevent the engine from starting. To keep this from happening, replace paper filters—or clean or replace foam filters—after every 25 hours of engine use.
The process for removing the filter depends on whether you are operating a riding or walk-behind lawn mower. For a riding mower, turn off the engine and engage the parking brake; for a walk-behind mower, pull the spark plug wire from the plug. Then, lift the filter from its housing.
The only choice for paper filters is replacement. If you’re cleaning a foam filter, wash it in a solution of hot water and detergent to loosen grime. Allow it to dry completely, and then wipe fresh motor oil over the filter, replace it in its housing, and power up the mower—this time to the pleasant whirring of an engine in tip-top condition.
Check the spark plug.
Is your lawn mower still being stubborn? The culprit may be the spark plug, which is responsible for creating the spark that ignites the fuel in the engine. If it’s loosened, disconnected, or coated in water or carbon residue, the spark plug may be the cause of your machine’s malfunction.
Locate the spark plug, often found on the front of the mower, and disconnect the spark plug wire, revealing the plug beneath. Use a socket wrench to unscrew the spark plug and remove it.
Check the electrode and insulator. If you see buildup, spray brake cleaner onto the plug, and let it soak for several minutes before wiping it with a clean cloth. Reinstall the spark plug, first by hand, and then with a socket wrench for a final tightening. If the problem persists, consider changing the spark plug.
Clear the mower deck of debris.
The mower’s deck prevents grass clippings from showering into the air like confetti, but it also creates a place for them to collect. Grass clippings can clog the mower deck, especially while mowing a wet lawn, preventing the blade from turning.
If the starter rope seems stuck or is difficult to pull, then it’s probably due to a clogged deck. With the mower safely turned off, tip it over onto its side and examine the underbelly. If there are large clumps of cut grass caught between the blade and deck, use a trowel to scrape these clippings free. When the deck is clean again, set the mower back on its feet and start it up.
Clear the vent in the lawn mower fuel cap.
The mower started just fine, you’ve made the first few passes, then all of a sudden the mower quits. You pull the cord a few times, but the engine just sputters and dies. What’s happening? It could have something to do with the fuel cap. Most mowers have a vented fuel cap. This vent is intended to release pressure, allowing fuel to flow from the tank to the carburetor. Without the vent, the gas fumes inside the tank begin to build up, creating a vacuum that eventually becomes so strong that it stops the flow of fuel.
To find out if this is the problem, remove the gas cap to break the vacuum, then reattach it. The mower should start right up. But if the lawn mower won’t stay running and cuts off again after 10 minutes or so, you’ll need to get a new gas cap.
Clean and refill the lawn mower fuel tank.
An obvious—and often overlooked—reason your mower may not be starting is that the tank is empty or contains gas that is either old or contaminated with excess moisture and dirt. If your gas is more than a month old, use an oil siphon pump to drain it from the tank.
(It’s important to be careful as spilled oil can cause smoking, but there are other reasons this might happen. Read more about what to do when your lawn mower is smoking.)
Add fuel stabilizer to the tank.
Fill the tank with fresh fuel and a fuel stabilizer to extend the life of the gas and prevent future buildup. A clogged fuel filter is another possible reason for a lawn mower not to start. When the filter is clogged, the engine can’t access the gas that makes the system go. If your mower has a fuel filter (not all do), check to make sure it’s functioning properly.
First, remove the fuel line at the carburetor. Gas should flow out. If it doesn’t, confirm that the fuel shutoff valve isn’t accidentally closed. Then remove the fuel line that’s ahead of the fuel filter inlet. If gas runs out freely, there’s a problem with the fuel filter. Consult your owner’s manual for instructions on replacing the filter and reassembling the mower.
Inspect the safety release mechanism cable.
Your lawn mower’s reluctance to start may have nothing to do with the engine at all but rather with one of the mower’s safety features: the dead man’s control. This colorfully named safety bar must be held in place by the operator for the engine to start or run. When the bar is released, the engine stops. While this mechanism cuts down on the likelihood of horrific lawn mower accidents, it also can be the reason the mower won’t start.
The safety bar of a dead man’s control is attached to a metal cable that connects to the engine’s ignition coil, which is responsible for sending current to the spark plug. If your lawn mower’s engine won’t start, check to see if that cable is damaged or broken. If it is, you’ll need to replace it before the mower will start.
Fortunately, replacing a broken control cable is an easy job. You may, however, have to wait a few days to get the part. Jot down the serial number of your lawn mower, then head to the manufacturer’s website to order a new cable.
Check to see if the flywheel brake is fully engaged.
The flywheel helps to make the engine work smoothly through inertia. When it isn’t working properly, it will prevent the mower’s engine from working.
If it is fully engaged, it can make a mower’s pull cord hard to pull. Check the brake pad to see if it makes full contact with the flywheel and that there isn’t anything jamming the blade so the control lever can move freely.
If the flywheel brake’s key sheared, the mower may have run over something that got tangled in the blade. It is possible to replace a flywheel key, but it does require taking apart the mower.
Look out for signs that the mower needs professional repairs.
While repairing lawn mowers can be a DIY job, there are times when it can be best to ask a professional to help repair a lawn mower. If you’ve done all of the proper mower maintenance that is recommended by the manufacturer, and gone through all of the possible ways to fix the mower from the steps above, then it may be best to call a pro. Here are a few signs that indicate when a pro’s help is a good idea.
- You see black smoke. The engine will benefit from a technician’s evaluation, as it could be cracked or something else might be worn out.
- Excessive oil or gas usage. If you’ve changed the spark plugs, and done all of the other maintenance tasks, and the mower is consuming more than its usual amount of oil or gas, consult a professional for an evaluation.
- The lawn mower is making a knocking sound. When a lawn mower starts making a knocking sound, something could be bent or out of alignment. It may be tough to figure this out on your own, so a pro could help.
- A vibrating or shaking lawn mower can be a sign of a problem beyond a DIY fix. Usually something is loose or not aligning properly.
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Lawn Mower Parts
Search and shop all the parts you need for your riding lawn equipment and Gator UTV including lawn mower blades, filters, belts, spark plugs, oil, and home maintenance kits.
Search part numbers and John Deere parts diagrams to identify exactly what you need to keep your equipment running smoothly.
Quick Reference Guides
As a John Deere owner, when it’s time to maintain, service or repair your equipment we have easy-to-use information sheets that keep your John Deere equipment running well.
Home Maintenance Kits
Feel confident in tuning up your lawn mower or garden equipment this season with our Home Maintenance Kits. Easily find the right product so you can DIY and save!
Looking for your Serial Number?
Finding your lawn mower’s model number and serial number is as easy as locating the identification tag on your machine. As seen in the example, the model number will be displayed below the MODEL heading (Example: Z235), and the serial number will be underlined on the top-right corner of the tag (Example: 130002).
If you’re looking for the engine number, that can be found directly on the engine itself.
Home and Garden, eat your heart out.
Get the latest on how to care for and enjoy your yard and garden. The articles and videos are informative and the ideas are amazing.
MowerPlus Mobile App
MowerPlus is the app you need to keep your John Deere riding lawn mower running well and your lawn looking great this season. The app tracks and records yard tasks and serves as a one-stop shop for seasonal care tips and maintenance activities. Know your mower and know how you mow with John Deere’s MowerPlus app.
The Right Part. The Right Price.
At John Deere, you get the value of choice for your maintenance and replacement parts for all makes and ages of machines – at any budget.
Genuine John Deere Belts Blades are your best choice for your newer machines.
Alternative Parts are an economical solution for your John Deere equipment.
The John Deere Easy Change 30-Second Oil Change System
Never drain engine oil again.
We’ve changed the oil change. Revolutionized it really. See how fast and easy changing your oil can now be on 100 Series Riding Lawn Tractors with the John Deere Easy Change 30-Second Oil Change System. Only from John Deere. Included on the E120, E130, E150, E160, E170, and E180 models.
Step One. Take it off.
Lift the hood. Make sure the engine is cool, then, twist to remove. It’s that simple.
Step Two. Twist and lock.
“Grab” the new Easy Change Canister, twist and lock into place. Make sure the arrow on your Filter System aligns with the arrow on your engine.
Step three. Done.
Close the hood and mow. John Deere recommends the Easy Change 30-second Oil Change System every 50 hours or at the end of your mowing season. Don’t drain engine oil ever again.
Draining engine oil is so 2017.
The engine modifications and new technologies are in. The re-envisioned oil filter with a media designed to resist breaking down in oil over time is here. The thousands of hours of testing are done. The end result is an all-in-one, oil and oil filter system like no other. The first of its kind. And thanks to the new John Deere Easy Change 30-Second Oil Change System (“System”), you’ll never have to drain the oil from 100 Series Riding Lawn Tractors again.
Here’s why: The new System captures contaminants and recharges your engine with nearly a quart (0.8qt) (0.76 l) of new oil. In fact, this System increases the amount of oil in the engine by nearly 40%. 2 Your engine likes that.
What do you mean, I will never have to drain oil from my engine again? How is that possible? The answer is simple. We have developed a better filtration system and filter design for our 100 Series Riding Lawn Tractors 1. This fully synthetic filter media has greater surface area which increases its capacity to hold harmful contaminants. What’s more, the filter media is designed to resist breaking down in oil over time. Which means you’ll get a cooler running engine. And a cooler running engine and better filtering helps increase engine oil life. John Deere’s recommended oil service for 100 Series Riding Lawn Tractors 1. is to change the System every 50 hours or once a season, whichever comes first. Remember, the System replaces a portion of your engine oil. And that’s plenty.
The System uses John Deere Turf-Gard Oil. Using John Deere Turf-Gard Oil ensures you are using the exact oil specified by John Deere engineers.
Testing. Testing. Testing. Thanks to thousands of hours of rigorous and extensive testing, you can feel confident your engine will run for years to come.
1 The John Deere Easy Change 30-Second Oil Change System is available on E120, E130, E150, E160, E170 and E180 Lawn Tractors today.
2 Compared to similar V-Twin engine models that do not have the John Deere Easy Change 30-Second Oil Change System. That includes equivalent Deere 2017 models and 2018 models without the System.
Frequently Asked Questions:
What is new with John Deere Riding Lawn Equipment?
We are excited about the exclusive John Deere Easy Change 30 second oil change system. Exclusive to John Deere and only available on certain models of the new 100 Series Lawn Tractors. These tractors are designed for ease of use for both operation and maintenance. The John Deere Easy Change System (“Easy Change”) allows the user to easily complete the recommended engine oil and filter maintenance in 30 seconds.
What is this new oil change system?
We changed the oil change. The all-in-one oil and oil filter system gives the owner the ability to change a portion of the oil and the filter in less than 30 seconds.
What happens to the rest of the oil in the engine when the Easy Change system is replaced?
The Easy Change system replaces.8 quart of oil. The remaining oil in the engine is refreshed by the charge of new oil included in the replacement Easy Change system. Combined with 40% more engine oil capacity, improved filtration and cooler running temperatures which help extend oil life, it is no longer necessary to remove and dispose of all the oil in your engine during service.
What makes the Easy Change system unique from other filters?
It is not just a filter. It is a newly developed technology system that allows a new “filter” to come already charged with oil and allows you to remove an existing filter and the contaminants inside without tools and without making a mess. Beyond the filter, technology within the canister and on your engine makes this possible.
Models with the Easy Change oil system use a fully synthetic filter that has more capacity to trap and hold contaminants. The larger surface area of the Easy Change canister acts like a radiator helping the oil to stay cool.
Does the Easy Change system somehow decrease the life of the engine?
The John Deere 100 Series lawn tractor models, with and without Easy Change, are specified for the same lifetime and are rigorously tested to the same standards to ensure the life of the tractor meets expectations.
Can I add the Easy change system to an existing tractor?
Because this system also requires unique features within the engine, the Easy Change system cannot be added to an engine that was not equipped with it at the factory.
Can I change all the oil if I choose to?
You could if you wanted to. There is an oil drain plug. It is not required for maintenance.
How often do I need to change the Easy Change canister?
Every 50 hours or once a year. The 100 Series Lawn Tractors with and without the Easy Change system have the same maintenance schedule.
What type of oil is recommended?
We recommend only John Deere Turf-Gard 10W30 Oil. The Easy Change canister comes pre-filled with John Deere Turf-Gard 10W30 oil.
How do I recycle the old oil?
Many local government recycling programs, authorized retailers, auto repair stations, and auto parts stores will puncture and recycle used oil filters and oil.
Do I ever need to add oil?
Yes. Consistent with our service recommendations for this product, you should check oil level daily and add oil if required.
Lawnmower Spits Gas Out of Fuel Cap: Reasons and Fixes
You’re mowing your lawn, and gas starts spitting out of your fuel cap. What causes fuel to sputter from a lawnmower’s gas cap, and can the issue be fixed?
One of the most common reasons gas spews from a lawnmower’s cap is overfilling the fuel tank. Other reasons fuel can eject from the gas cap include problems with the cap itself and more serious internal engine problems.
Read on to find out if your specific fuel issue can be fixed quickly and cheaply or if it’s a sign of more serious hidden damage.
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Fuel Cap Leaks Caused by Overfilling the Tank
Every lawnmower comes with a manual that tells you how much gas you can put into your tank. Pay close attention to what your user manual says, as well as any raised or printed indicators on or in the fuel tank if you don’t; you can run into more problems.
Like any gas-powered tool, Lawnmowers have extra space in their fuel tanks because fuel expands when heated (source). If you overfill your tank, the gas will expand, causing immense pressure that becomes so great that it pushes gasoline out of the fuel cap’s vent.
If you check your fuel level and it’s above the fill line, and you have fuel escaping from the cap, your problem is most likely due to an overfill.
To fix your problem, you will have to:
- Turn your mower off
- Let the fuel in the tank cool down
- Place a bucket or gas can under the fuel line
- Unhook the fuel line from the gas tank
- Drain the excess gas from the tank until levels fall under the fill line
- Reattach the fuel line
- Move the excess gas to a safe place
- Start the mower up again
This YouTube video gives a great demonstration of how to check the fuel tank for proper venting:
Fuel Cap Leaks Caused by a Broken Cap
If you always fill your gas tank according to your manual and keep your gas cap clean, then your problem may lie with the integrity of the fuel cap.
The best way to check if you have a bad gas cap is by examining it closely. Do it have:
- A crumbling seal?
- Cracks in the cap?
- Only a plastic pin on the underside of your cap? (Tecumseh Brand)
- Problems with tightening the cap?
- A smell of gas coming from your mower?
- No clicking sound when you screw the cap into the fuel tank?
If you encounter any of the above issues, then your cap is due to be replaced. Check your owner’s manual to find information on the correct cap to use or tell your local mechanic the make and model of your lawnmower.
Depending on the model of your mower, some gas caps will make a clicking sound when sufficiently tightened.
Remember, even if your fuel cap is new, it can still have problems from the manufacturer so double-check the above signs even with cap is brand new.
Other Causes of Gas Spitting From A Lawnmower Fuel Cap
The fuel-spewing issues can also occur due to an increase in vibration when using the mower. Usually, the problem is simply compounding the existing issue with a gas cap but let’s go over these quickly.
Any lawnmower will have some degree of vibrations. Naturally, the problem occurs when the motion is exacerbated by things such as:
- Loose bolts or mounts
- Broken parts
- Unbalanced blades
- A bent crankshaft
These parts can range from cheap to really expensive to fix, but you don’t want to keep running your mower without fixing these issues. Allowing your mower to vibrate excessively while you use it can further damage it, and you can put yourself at risk of bodily harm since parts can dislodge from the mower.
Loose bolts and mounts are easy to fix if you have a socket wrench, so you can tighten those at home. You can also fix unbalanced blades yourself as long as they’re not bent.
To fix your blade problem, check and make sure the blades are screwed onto your mower tightly and correctly. If the issue is not with how the blade is installed, you will have to do the following to fix it:
- Make sure your lawnmower is off
- Unplug your spark plug
- Take the blade off
- Hang your blade off a nail on your wall
- Sharpen the side of the blade that hangs lower on the nail
- Reinstall your blade
- Plug your spark plug back in
- Turn your mower on
This should immediately fix the vibration issue.
If you’re experiencing issues with other broken parts of the mower, like the crank shaft, contact a mechanic. Crankshafts are hard to fix if you don’t have the right tools.
Can You Use Your Mower Without a Fuel Cap?
After reading all of the above, you might be wondering, can you use your mower without the fuel cap? It definitely seems like a quick solution to most of the pressure issues we’ve talked about! While some people say you can run your mower without a gas cap, we do not recommend it.
If you run your mower capless, you’re more likely to spill gas as it sloshes around in the tank, and it might go undetected as you mow. This is a fire hazard (source).
Gas caps also keep sediment and debris out of your gas tank. Sediment in the tank can keep your lawnmower from starting or even damage the engine.
Finally, gas caps keep harmful fumes from escaping.
Overall it’s just best not to risk it.
A problem of gas spitting out the gas tank of a lawnmower is almost always an indicator that there is an issue with the gas cap. Even when the tank is overfilled, a properly fitting cap should prevent this.
Clean it, make sure it isn’t cracked, and if necessary, replace it. Do not ignore this issue or simply run the mower without a gas cap. It’s there for a reason. Purchase a replacement gas cap online (link to Amazon) or check your manufacturer’s website.
Paul has a two-acre yard on red clay soil in Southeast Texas. He knows exactly what the challenges are to nurturing a thriving yard in difficult soil.Paul takes a practical approach to yard improvement and enjoys putting best practices and “golden rules of lawn care” to the test.
Temporary Lawn Mower Gas Cap (A Few Ideas)
If you’ve lost the gas cap for your lawn mower, have searched “can I use my lawn mower without a gas cap” and realized it’s not a good idea, what options do you have? Obviously buying a replacement is the most logical thing to do. But what if you really need to mow your lawn right now and have no time to run to the store. In that case, creating your own temporary lawn mower gas cap is your best option.
A temporary gas cap can be made out of a whole manner of things you may have lying around the house, including aluminum foil, plastic cap, part of a plastic bag and cork. It may also be possible to borrow the gas cap from other power tools you own.
Things You Could Use to Create a Temporary Lawn Mower Gas Cap
The key word here is “temporary”. None of these ideas are supposed to replace your gas cap. They are temporary solutions that will allow you to mow if you’re in a bind, but a replacement cap should be sourced as soon as possible.
That said, here are a few ideas for things you could use.
It’s very likely you have some of this in the kitchen. Grab a roll, tear off a small piece that is big enough to cover the opening to your gas tank, and then secure it in place with a rubber Band.
Have a look in the kitchen and see if you have any plastic bottles or other containers that have a cap big enough to cover the opening to your mower’s gas tank. You could also have a look in your shed or garage. Sometimes the cap for a gas can will actually be the perfect fit.
If you find one, you’ll need to use a rubber Band or some duct tape to secure it into place.
This is similar to the foil. If you don’t have any of that, you can take a plastic bag, cut a piece off, cover the tank opening and fix it into place with a rubber Band. Not ideal, but it’ll seal the opening for the time being.
A lot of corks (like those from wine bottles) are unlikely to be thick enough to cover the opening to your gas tank. But if you have a cork that’s bigger than that, it might just do the job.
Caps from Other Gas Powered Tools
Do you have any other gas-powered tools sitting in your shed or garage? Maybe a hedge trimmer, weed wacker, scarifier…Whatever tools you have, check the gas caps on them. It’s possible that you might get lucky and one of them might fit (or at least cover) your lawn mower gas tank.
Don’t Use a Rag
If you’ve been doing some research online, it’s possible that you will have come across suggestions to stuff a rag or some cloth into the gas tank opening to block it up.
I personally wouldn’t recommend doing this. The problem I see is that cloth or rag can soak through with gas and may start to drip onto the deck and your grass.
So if you want to avoid a lawn mower on fire and dead patches of grass on your lawn, stick to the other suggestions above, or better still, go buy a replacement now.
Using a Temporary Lawn Mower Gas Cap: Final Thoughts
Before you run off to go and create your temporary lawn mower gas cap, here are a few final thoughts about doing this:
- Only Use a Temporary Gas Cap if You Have to – If you do create your own gas cap, no matter how well-crafted you think it is, there’s always going to be a risk to using your mower like this. So only mow your grass with a temporary cap if it’s absolutely necessary. If there’s any possibility of delaying your mowing session until you can buy a replacement gas cap, please do. That’s the best way to ensure your safety.
- Make Sure It’s “Just This One Time” – If you create a temporary gas cap and use your mower with it fitted and everything goes well, don’t fall into the trap of thinking it can serve as a replacement. A temporary cap can help you when you’re in a real bind and must get the lawn mowed (maybe you’re going away for summer vacation tomorrow and the store is closed today). But make sure you order a replacement and have it fitted by the next time you mow.
- Go Slow and Steady – A temporary lawn mower gas cap is not going to seal the gas tank as well as the proper cap will. So take a little extra care when mowing, going slower than normal to minimize the chances of the gas moving around in the tank and up towards the opening.
- Don’t Mow with a Full Tank – The fuller your tank, the more chance there is of you spilling gas with a temporary cap fitted. So if your tank is full right now, I’d recommend you remove some of the gas before you start.
Above all, be safe and sensible if you decide to mow with a temporary gas cap in place.
About Tom Greene
I’ve always had a keen interest in lawn care as long as I can remember. Friends used to call me the “lawn mower guru” (hence the site name), but I’m anything but. I just enjoy cutting my lawn and spending time outdoors. I also love the well-deserved doughnuts and coffee afterward!