9 Fixes For When Your Lawn Mower Won’t Start. Gas in lawn mower

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.)

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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.

Do You Mix Oil and Gas for Lawnmower? (What You Need to Know)

If you’re a new lawnmower owner, you might be wondering, “Do you mix oil and gas for a lawnmower?” And if so, what’s the oil and gas ratio you should add?

The short answer is that 2-cycle engine lawnmowers require a gas and oil mixture for fuel, while 4-cycle engines run on straight gasoline. The most common gas and oil mix ratio for lawnmowers are 50:1, but you’ll want to refer to your owner’s manual for your particular model’s recommended gas and oil mixture ratio.

This can be confusing, primarily if you’ve never owned a lawnmower.

In the following paragraphs, we’ve provided all the information you need to help you answer any questions you may have regarding this topic, so stick around.

Do You Mix Oil and Gas for Lawn Mower?

You might be able to mix oil and gas and add them to a lawnmower. However, it’ll all depend on the type of engine your mower has.

Some engines allow you to add oil and gas together, while others will only work if you add them separately. This is why it’s essential to know the type of engine your unit is housing before you start mixing oil and gas.

What Engines Can You Mix Gas and Oil In?

Lawnmowers typically house one of two types of engines. The first is the two-cycle/cylinder engine, and the second is a four-cycle/cylinder engine.

If you own a two-cycle engine, you can add a mix of gas and oil. But, per contra, if you own a four-cycle engine, you need to refrain from mixing the gas and oil, or it may damage your engine.

If you checked and saw that you own a four-cycle engine, you’ll also notice that there are different tanks and openings where you can add oil and gas separately.

How to Know If You Own a Two-Cycle or Four-Cycle Engine?

There are many ways you could differentiate between a two-cycle engine and a four-cycle one. The most common way is to check the engine’s port. If it only has a single opening, then it’s a two-cycle engine, and you can add your oil and gas mix without any worries.

If you find two ports separating two tanks, then it’s a four-cycle engine, and you’ll need to add your gas and oil separately.

Another way to recognize the engine’s type is by checking if there are any warning stickers against mixing oils and fuel. You might also find them already labeling the engine as either two-cycle or four-cycle—they can also be called two-stroke or four-stroke, respectively.

If you have any trouble finding out the type directly from the engine, you can check the user’s manual that came with the mower. The manufacturer will always mention whether it’s a two or four-cycle engine in the manual.

What Is the Correct Oil-Gas Ratio to Add to Your Lawn Mower?

If you checked your engine type and found it to be a two-cycle, you can now add in your gas and oil mix. But before you do, you need to make sure you’re adding the appropriate amount.

The amount of gas and oil mixture you add will depend on how much your engine requires. Some two-cycle engines use a 50:1 gas to oil ratio; others use 40:1. Some older models may use 32:1.

You can check the ratio your engine uses by checking the port. Most engines will have the ratio written on the cover. If it’s not there, you’ll find it written in the user’s manual.

If you found that your engine uses a 50:1 ratio, you’ll need to mix around 2.6 ounces of oil with 1 gallon of gas.

If your engine uses a 40:1 ratio, add 3.2 ounces of oil to 1 gallon of gas. The 32:1 ratio will need 4 ounces of oil added to 1 gallon of gas.

What Type of Oil and Gas Should You Use?

Most manufacturers will include what type of oil and gas you should use on your grass cutter in their manuals. So checking the manual is a must.

If you have any trouble with the user’s manual, you can refer to the recommended type for each engine.

It’s advised for both two-cycle and four-cycle engines to use an unleaded gas with a minimum 87 octane rating and a maximum of 10% ethanol.

Most gas stations sell fuel with more than 15% ethanol, so be sure to check the ethanol percentage when buying your gas. It shouldn’t exceed 10%, or it may damage your engine.

As for the oil, there are oils available specifically for two and four-cycle engines, respectively, so it’s best to use them for your lawnmower depending on the type of engine you have.

How to Mix Your Gas and Oil Before Use?

Now that you have the gas and oil you need, you can start preparing your mix to use on your mower. Refer to the previous section to know the correct gas to oil ratio you should use.

The first thing you’ll need to do now is to prepare an empty gas bottle. Then, make sure it’s completely clean before adding the new gas.

Afterward, you can add in your oil and then start mixing. You can mix it up by stirring or shaking the bottle well. That should get your mixture ready for use.

Please note that you’ll need to use this gas-oil mixture for one month, or it’ll start losing its effect.

What Happens If You Add the Oil and Gas Mix to a Four-Cycle Engine?

All the previously mentioned steps are specifically for two-cycle engine use. Now, what if you accidentally added this newly made mix into a four-cycle engine instead?

As long as you notice the mistake quickly, there shouldn’t be much of a problem. You’ll need to drain all the mixture you just added out and replace it with the correct gas or oil per tank.

If you turn on your mower before you drain the mixture, it may, unfortunately, be too late, and you’ll start noticing your lawnmower smoking up.

Using an oil and gas mix on a four-cycle engine will cause it to overheat and eventually break down. So it’s best to be entirely sure of which type of engine your lawnmower has before use to avoid causing any damage.

How Often Should You Change Your Gas and Oil?

It’s recommended to replace your gas and oil mix after three weeks to one month of use. You can wait until two months to replace it, but it won’t be as effective anymore.

That’s why it’s better to use a new mixture every three weeks to get the best results and make sure you don’t exhaust your engine.


Lawnmowers tend to have two types of engines, and depending on which type they have, they can use a gas and oil mix, or you’ll need to separate the oil and gas from each other.

If you have a two-stroke engine, you can mix gas and oil without any problems. However, if your mower is equipped with a four-stroke engine, you can’t mix gas and oil. That’s why you need to know the difference before using it.

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After a long winter’s rest, your mower may need a nudge before springing to life. Follow these simple steps for starting a lawn mower—and learn how to troubleshoot a mower that won’t run.

By Bob Vila and Tony Carrick | Updated Mar 24, 2023 12:54 PM

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Unless you’re planning to hire a lawn care company to handle your yard maintenance, you’ll need to learn how to start a lawn mower if you want to maintain a well-kept lawn. In addition to learning the basics, it’s also crucial to understand what factors influence how easy (or how difficult) it is to start a mower, including gas and oil levels and the condition of the spark plug and mower deck. The methods below will walk you through starting a lawn mower and help you troubleshoot any problems you may encounter along the way.


Below is the gear you might need to get your lawn mower up and running. It’s more than likely, however, that you won’t need more than a few items. The equipment you use will depend on whether there’s anything wrong with the mower, and the troubleshooting tips you follow below.

Before You Begin

Before starting up the mower, take a moment to walk your yard and clear it of any sticks, toys, and other obstacles that could damage your mower blade. Make sure that you have gas, oil, and other materials listed above close at hand.

Starting a Lawn Mower

Whether you’re new to lawn mowers, know how to use a lawn mower but have forgotten how to start one after a long off season, or are dealing with a mower that is refusing to start, these steps will help you get that mower up and running.

STEP 1: Check if your mower has gas and oil.

Look for the large black cap on the top of the mower engine (it should have an imprint of a gas tank on it). Unscrew the cap and peer inside to see if you need to add gas.

The cap for the oil pan will be on the opposite side of the engine. Look for an imprint of an oil can on the cap. Unlike the gas cap, which screws off, you should be able to remove the oil cap by giving it a half turn counterclockwise. You’ll know you have the right one when you pull the cap out and there’s a dipstick attached to it. Wipe the dipstick clean with a rag, replace it, then pull it out again and check the oil level. The oil level should be between the two marks on the stick.

STEP 2: Add gas and oil if needed.

If you’re adding gas, use the same unleaded gas you put in your car, and not the 2-stroke gas/oil mix that other yard equipment uses. Most push mowers hold between 1/4 and 2 gallons of gas. Use a funnel to avoid spilling the gas as you add it to the tank.

If you need to add oil, check the lawn mower’s user manual to see what oil weight the manufacturer suggests. If the manual does not specify an oil type, use SAE 30, the best option for engines that operate in warmer temperatures.

STEP 4: Prime the engine.

Priming the engine is necessary only if the lawn mower has not been used for a prolonged period of time (over the winter, for instance). Once you’ve attended to the mower’s gas and oil, press the primer button three to five times in order to channel gas into the engine. If you’ve used the mower recently, you can probably skip this step.

STEP 5: Pull the starter cord.

Notice how there are two handles on the lawn mower, each running horizontally only inches apart from the other. Press and hold these handles together, keeping them together as you pull the starter cord. Do so quickly and with considerable force, and the mower engine should to turn over. Sometimes it can take several attempts before pulling the starting rope achieves the intended result: a purring motor.

Troubleshooting Lawn Mower Issues

If you’ve already checked that the mower has ample oil and gas and it still won’t get up and running, it’s time to start troubleshooting. Here are the steps you should take to determine why your lawn mower won’t start:

Check the carburetor.

If you have already confirmed that there’s oil and gas in the mower, but the engine still refuses to start, it’s possible that either the carburetor has flooded or the cylinder has become soaked with gas. (The smell of unburned gas is a telltale sign.) Leave your mower on level ground for at least 15 minutes, which should allow enough time for the gas to evaporate from within the mechanism.

Check for old gas.

If you are starting your lawn mower for the first time after a long off-season in the garage, gas that was left in the machine may have gone bad. If you suspect this is the case, observe the mower the next time you try to get it going: Does it appear to start up, then quickly stall out? The fix is simple: Siphon the old gas and replace it with fresh fuel.

Check for spark plug problems.

While the spark plug’s location can vary depending on the mower, most of the time you’ll find it at the front of the engine. Pull the rubber cap off the spark plug. If you spot debris on the end of the spark plug or inside the cap, wipe it clean with a rag.

Unscrew the spark plug using a spark plug socket and socket wrench. Clean the electrode on the end of the spark plug with a wire brush and brake cleaner. If there are a lot of deposits built up on the spark plug or if it’s cracked, you’ll need to replace it with a new one. Otherwise, screw the spark plug back in, tighten it with the socket wrench, and attempt to start the engine.

Clean the grass clippings out of the mower deck.

Lay the lawn mower on its side so you can access its underside. Use a pry bar to dislodge any built-up clumps of grass from the mowing deck. After getting rid of the large pieces, use a garden hose to spray the deck. Give it a good scrub with a stiff bristle brush to remove stubborn debris sticking to the deck. Rinse with the hose, then turn the mower back upright and attempt to start it.

If you’ve tried these methods and your lawn mower still won’t come to life, refer to our detailed guide on what to do when your lawn mower won’t start.

Final Thoughts

While starting a lawn mower isn’t a complicated task, you can run into problems if the mower is low on gas or oil, has a bad spark plug, or if clumps of grass are clogging the mower deck and blade. The troubleshooting methods will help you learn how to turn on a lawn mower and get it back in action. In the event your best efforts to start the mower fail, there may be a larger issue with the lawn mower engine. In that case, you’ll need to seek out a lawn mower repair shop for help.

For more lawn mower advice, check out our video on the most common mowing mistakes almost everyone makes.

Is It Bad for A Lawn Mower to Run Out of Gas?

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Spring is here. The April sun melts the snow and ice, and before you know it, it’s time to prep your yard for summer. That means busting out the lawn mower to give your grass a much-needed trim.

Unfortunately, lawn mowers don’t have fuel gauges. So, it’s difficult to tell when it’s time to fill up on gasoline. You’d think that the solution to your problem is simple, right? You simply have to refill the tank, and you’re good to go. But, for some reason, your mower won’t start even after you fill it.

Don’t worry. Keep reading to learn what the problem may be and how to get your mower running like new.

Your Lawn Mower Has a Dirty Carburetor

So, your lawn mower isn’t starting after running out of gasoline. One of the first things you should check is your carburetor.

When you run through your gas tank, your mower will start sucking up the debris that’s sitting at the bottom of your fuel tank. While your mower should have a fuel filter, the sediment lying at the bottom of the tank is usually so fine that it can get through the filter.

All you have to do is clean the carburetor bowl to fix this problem. Typically, you can locate the carburetor bowl just behind your mower’s air filter.

If draining the carburetor bowl doesn’t work, you most likely have a failed carburetor that needs to be replaced for your engine to start correctly.

There Is an Airlock in Your Lawn Mower’s Fuel System

An airlock is one of the common causes why your mower won’t start after running out of fuel.

An Airlock occurs when air replaces fuel in the fuel lines. As you refill your fuel tank, you could push the air towards your mower’s carburetor, which keeps the new fuel from reaching the engine.

To fix this problem, ensure you fill your fuel tank to the very top with new fuel or try draining the carburetor bowl as described above.

You’ve Filled Your Lawn Mower with Bad Fuel

Another reason why your mower may not be starting is that you refilled it with bad fuel. If not treated with stabilizers, most fuels only have a shelf life of about three to six months. So, if you’re using gasoline from last summer, you may want to replace it.

If you believe bad fuel is the culprit, drain your fuel tank and replace it with new fuel.

Refill Your Lawn Mower Properly with EZ-POUR /h2>

Are you fresh out of fuel? Do you need a safe, reliable, and clean way to refill your lawn mower? Well, EZ-POUR has the solution for you. To fill your lawn mower and other small lawn equipment, we recommend using our Replacement Fuel Spout Vent Kit.

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Lawn Mower Storage: Why Draining The Fuel Tank Is A Mistake

Wondering how you can ensure your lawn mower and outdoor power equipment will be ready to roll when the grass turns green?

If you’ve checked your manufacturer’s guide, you’ve probably seen a suggestion to perform some preventive maintenance prior to storage. This is always a good habit to get into. Some manufacturers will also recommend running your equipment dry before putting it away for the winter.

While draining the fuel tank may sound like a good idea, it could harm your engine.

Running a lawn mower dry will make it harder for it to fire right up when it comes time to take it out of storage. This is true of all your outdoor equipment and tools, from mowers and blowers to trimmers and chainsaws.

Lawn equipment relies on three basic elements to work. If you don’t have all three, your engine will not run:

Clean air will always be available if you take time to clean or replace your air filter. And a clean, properly-gapped spark plug usually takes care of the spark.

But fuel? If you don’t maintain components that help properly distribute gas at the right time and in the right amount, your equipment might not perform well. In fact, it may not run at all.

Draining the tank harms your lawn mowers carburetor

Draining the tank harms the “heart” of your equipment. Think of one of the most important organs in your body: your heart. The lawn mower carburetor is, in many ways, your engine’s “heart.” It blends air and fuel and circulates these elements into an engine’s cylinders.

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Each time you drain the gas tank, you inadvertently put stress on your equipment’s critical “organ.” Here’s what happens:

  • Draining fuel allows oxygen to enter the lawn mower’s carburetor.It’s impossible to get every last drop of gasoline out. When oxygen attacks the small fuel droplets left behind, it causes gum and varnish. If this debris settles in the wrong place, such as a needle valve tip, the carburetor will need cleaning to work properly.
  • Where there is air, there is water (damage).Allowing your gas tank to sit empty for long periods leaves a huge area for water vapor to condense. When moisture collects, it can trigger corrosion in the tank, fuel lines, carburetor and cylinders, and can even cause catastrophic engine failure if a big “gulp” is taken into the engine all at once. (If your mechanic says there is “white rust” in the carburetor, this is why.)
  • Fuel system plastics and rubbers are designed to live in fuel.These parts can become brittle and crack when exposed to air.

What to do instead: Avoid risks with gas stabilizer.

Manufacturers sometimes recommend draining the tank to winterize a lawn mower because the worst thing you can do is leave old fuel in an engine during long periods of storage.

You may have followed this advice in the past without noticeable issues, but that doesn’t mean you’re in the clear. If draining the tank becomes a yearly habit, there’s a good chance you’re shortening the lifespan of your lawn mower and other tools.

There’s a much easier way to properly store your lawn equipment. To avoid damage, simply use a quality fuel stabilizer and fresh fuel before putting equipment away for the season.

Here’s how to winterize a lawn mower correctly

Step 1: Buy and stabilize fresh fuel for maximum protection. Adding fuel stabilizer to old fuel will stop it from degrading further, but the fuel may already have broken down.

Step 2: Fill your tank 95% full with fresh, stabilized fuel. Leaving a little room prevents the fuel from expanding and spilling in warmer weather, and reduces the risk of water vapor that can condense and contaminate fuel.

Step 3: Run the engine for a couple of minutes. This gets the stabilized fuel into the carburetor and fuel lines.

While you should still consult with your manufacturer for product-specific equipment and engine maintenance tips, these simple steps apply to all engines, big and small. A few minutes on each piece of yard equipment can save hours when the grass starts growing and the season kicks off in spring.

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