9 Fixes For When Your Lawn Mower Won’t Start. Bad gas 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.

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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.

Small Engine Diagnosis. Bad Gas!

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.

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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.

Top 5 Ways To Fix A LAWN MOWER That WON’T START (Fix It In Minutes)

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.

Common Engine Issues and Solutions for Lawn Mowers

Owning a lawn mower is like owning a vehicle, sometimes you will experience common issues that are just a part of ownership. Below we will cover a few common engine issues such as what to do if you put the wrong fuel in the fuel tank, what happens if there’s water in the fuel and more. Along with these issues we will also review some solutions to ensure any engine issues are caught in a timely manner and can be fixed properly.

What happens when I mix regular gas with diesel fuel or kerosene in my lawn mower?

Sometimes mistakes happen! If you mess up and put diesel into your gas lawn mower, you can still save your lawn mower. Lawn mowers are low compression so a little bit of diesel shouldn’t hurt anything too much. However, there is a risk that it will cause the mower to smoke rather badly. The best thing to do is to drain your tank immediately, refill it with gas and replace the fuel filter. Once you do so, you should be good to go and can continue mowing. It may smoke for a few minutes as it clears out the remaining bad fuel but should clear up quickly.

It is not recommended to add kerosene to your gas lawn mower, but we also understand mistakes happen. If a little bit of kerosene is mixed with your regular gas, there will not be any noticeable short-term effects. If there is around 15-20% kerosene in your gas tank, your mower is going to run rough at some point, then quit running all together. Repairs will potentially be needed beyond removing the bad fuel and putting in a clean fuel filter.

The best practice is to have multiple fuel cans, each for a specific fuel type. Color coded cans are available (red for gasoline, yellow for diesel, and blue for kerosene), or you can label them with a permanent marker. It’s also a good idea to have a separate can for mixed fuel used in trimmers or chainsaws.

What happens if there’s water in my gas lawn mower engine?

Springtime is a very common season to find water in your mower from condensation in the gas tank. If this water is not addressed, it can get into your lawn mower’s engine and cause some major performance problems. Not only do you risk performance problems, but you also risk some major long-term damages as well. Some of these long-term damages include corrosion in the tank, carburetor and fuel lines. When excessive corrosion happens to these parts of the lawn mower, it becomes very costly to repair.

If water does happen to occur in the engine oil, you can drain it and avoid long-term damage. To drain the water, you will need to start with the crankcase on 4-stroke engines. If water comes out with the oil (it will look milky in color), you will need to add some light oil, turn the engine over a couple times using the starter, and drain it again. Remove the spark plugs first, to discharge any oil from the cylinders and to make sure it does not start during the process.

What does it mean if my lawn mower is smoking?

Sometimes you will notice your lawn mower is putting off black exhaust smoke. The gasoline to air mixture is regulated in the lawn mower’s carburetor. If there is not enough air getting into the carburetor, then there is a higher ratio of gasoline which results in black exhaust smoke.

If your lawn mower does start smoking like this, you do not need to panic. The most common cause of a smoking lawn mower is a clogged or dirty air filter. When the air filter is not clean, the carburetor is unable to pull the proper amount of air in to keep the correct ratio of gasoline to air. Once the mower is shut off, check and replace the air filter and give it another try.

Routine maintenance (at least once a year) is key to avoiding many issues. A fresh oil change and new filters are inexpensive, and far less than major repairs. Consult your operator’s manual for a list, or contact us for assistance.

Where can I find lawn equipment maintenance and repair services?

Finding lawn equipment maintenance and repair services for equipment does not have to be time consuming or overwhelming. The expert technicians at Koenig Equipment are trained to fully inspect your mower and repair any and all issues so schedule the service you need today.

How To Start A Lawn Mower With Old Gas? Easy Tips Tricks From The Experts

Keeping a lawnmower in your tools is a must if you occasionally perform landscaping on your lawn. Most people store their lawnmowers in a shed over the winter and begin using them again once spring has passed. However, it is not as easy as you may expect to start up your lawn mower again after a long period of storage and inactivity. Why? Read on to find out our tips for starting a lawn mower with old gas!

The first thing that comes to mind when you think of goods with a shelf life is probably food that spoils or otherwise goes bad. One thing that you probably don’t give much thought to is gasoline; however, gasoline does deteriorate with time. If you put old gas in your lawn mower, it may not work properly or even refuse to start.

A lawn mower containing old gas must be drained and refilled with new gas. Also, its fuel filter and fuel lines need to be examined for fuel restrictions. In most cases, the carburetor is likely to be blamed if a lawn mower won’t start due to old gas. So, to start a mower with old gas, you must clean, restore, or sometimes replace it.

Having said that, there are a lot of other things that could be preventing a lawn mower from starting besides old gas. For instance, one of the most common reasons why lawn mowers don’t function is because their owners store them in places with high humidity.

So, if your lawn mower won’t start and is purring like a cat, here are some tips to get it going.

Reconditioning Old Gas

Ideally, you should drain and refill the gas tank on your lawn mower with fresh gas if you have not used it for a while. But sometimes, there might be an emergency. So for old gas, if you’re in a position where you really have to use it, there is a fix!

According to the Georgia Department of Natural Resources, if you have an old gas container lying around and aren’t sure what to do with it, you can recondition the gas so that it can be used in your lawn mower. However, different states could have different restrictions regarding who is allowed to recondition gasoline.

Nevertheless, conditioning old gas involves passing it through a filter made of cotton, nylon, or some other material having a finely woven structure and then combining it with new gasoline in a specific ratio. However, keep in mind that this reconditioned gas is only suited for use in lawn mowers that have engines equipped with carburetors.

It should not be used in vehicles that use fuel injection systems!

Fixing A Mower With Old Gas

If you have been using old fuel in your lawn mower and it won’t start, you will need to clean off the built-up residue that is preventing the engine from functioning correctly.

For this purpose, it is imperative that any gasoline that may still be present in the tank be drained using a siphon before attempting to use the mower again. Doing so will cause the original issues to appear again, and you will have to start over. This may also sometimes necessitate removing the carburetor and cleaning it, but that will depend on the type of mower you have and the amount of residue and silt present in the gas.

In some cases, the fuel line may also need to be replaced if it becomes clogged.

Why Is Old Gas Bad For A Lawn Mower?

If you put old fuel in your lawn mower, you could end up with a range of issues. As time passes, the volatility of the gasoline decreases, which can cause your mower to not run as smoothly and, in some circumstances, to splutter or stop working altogether while in use.

Things could get even worse during the humid conditions, when water makes its way into the fuel tank of the lawn mower. With time, it may become increasingly difficult to start your mower as a result of sediment and other deposits that have accumulated in the carburetor and fuel line. And if the situation persists, the mower may not be able to start at all.

Why Does Old Gas Goes Bad?

Several different things contribute to the breakdown of gasoline. Some additives, such as detergents, degrade over time and produce sediment.

Likewise, alcohol-based octane boosters, which enhance the volatility of the gasoline, evaporate over time and leave the remaining gasoline unable to ignite. Furthermore, moisture in the gas tank of a lawn mower can cause droplets of water to form, which then combine with the gasoline and contribute to the deterioration of the fuel.

Depending on the gasoline formulation, this deterioration can take place in as few as thirty days. However, the gasoline that has been properly stored can remain usable for up to a year and up to three years if it has been treated with gasoline stabilizers.

Other Issues That Prevent A Mower From Starting

Sometimes the issue is not the old gas that is preventing the mower from starting or working properly but other old or broken parts that are mentioned below:

Clogged Or Broken Fuel Cap

It is possible for the fuel cap to break or plug, stopping it from venting adequately. A vacuum develops in the gasoline tank when air cannot pass through the vent.

Due to the presence of this vacuum, the fuel will not be able to move freely from the tank to the engine. If you start and stop the lawnmower with the gasoline cap on and off, you’ll be able to tell whether or not the cap is in good working order.

If your lawnmower starts running with the fuel cap off, once the air is let into the fuel tank but stops operating after the fuel cap has been installed, you probably have a faulty fuel cap. In such a situation, changing the cap is a good idea.

A Bad Fuel Pump

If you have a lawn mower with a carburetor that is higher than the gasoline tank, you will require a fuel pump that can work against the force of gravity.

And, your lawn mower will not start if the fuel pump breaks or stops working correctly.

You can test the fuel flow out of the pump by detaching the gas line from the carburetor and placing it in a bucket to collect fuel. Turn on the lawn mower, and while it’s running, keep an eye out for a continuous or pulsating flow of fuel coming out of the line.

The fuel pump should be changed if the rate of fuel flow is low.

Utilize Ethanol-Free Fuel

If you are careful about what you use to try to restart the lawn mower, you might want to think about using ethanol-free gasoline. Ethanol-free fuels have a somewhat higher price tag, but they come with the additional perk of negating the requirement to clean the fuel tank before putting it away in the garage or shed.

Another advantage of using gasoline that does not include ethanol is that it requires very little maintenance and can be used immediately after the mower is turned on, even if it has been idling or sitting in a shed for a while.

Avoid Flooding The Carburetor

When there is a strong odor of gas coming from the carburetor, this is typically an indication of a significant issue known as carburetor flooding. In such instances, it would be best if you waited a short while before attempting to start the lawn mower once more.

If the engine has been sitting for an extended period, you should probably avoid flooding the carburetor before attempting to start it. This is a very common error that individuals make when starting their lawn mowers after a long period of inactivity.

When you try to start the lawn mower, you need to pay attention to the sounds and odors it produces while starting up. If the stench of the gas gets too potent, you must instantly cease trying to restart the lawn mower and fix the underlying issue.

How To Start A Lawn Mower With Old Gas?

The following are some additional suggestions for starting a lawn mower that has old gas and getting it roaring once again to mow your lawn.

Remove The Old Gas

Even though it is strongly suggested that you empty the fuel from your lawn mower before keeping it to rest for extended periods of time, not many people realize this (which is probably why you’re reading this piece). If you let gas sit in your lawn mover for an extended period of time, residue will form as a result of the gas’s breakdown.

To find out how to service your lawn mower and clear out the gasoline tank, look in the manual. You must ensure that all the debris in your tank is removed before filling it again. Clean the tank as thoroughly as possible if there is any residue within it.

Check If The Fuel Line Is Clogged

Check to see if there is any debris blocking the gasoline line next. Once more, old fuel might leave behind gummy deposits that will limit fuel flow via your lawn mower’s fuel lines. To do this, position a container beneath the gasoline line so that it can collect fuel as it comes from the line. Now start the mower and see the flow.

If the flow is insufficient or there is no fuel coming, you have a clogged fuel line.

And, if the fuel line is clogged, you can either replace it with a new one or push compressed air through the line to clear out the obstruction. Once done, turn on the gasoline supply and test your lawnmower to see if it starts and operates normally.

If it does not, proceed with inspecting and cleaning the fuel filter.

Examine Clean The Fuel Filter

Dust and old gasoline that has been lingering in your mower can block your fuel filter. When unclean and sticky deposits leak from the gasoline tank, the fuel filter will not let them pass through. If the filter gets clogged, less gas can travel through the fuel lines, making it nearly impossible to start your lawn mower.

In the event that the fuel filter is blocked, you should replace it with a new filter. When you are putting in the filter, make sure you pay attention to the arrow on its side.

Proper installation of an inline fuel filter requires positioning it between the fuel lines with the arrow pointing in the direction of fuel flow.

Check The Spark Plug

If you have already cleaned out the tank, fuel lines, and fuel filter on your lawn mower and added new fresh gasoline, but it still won’t start after, you need to make sure that the spark plug hasn’t become corroded or damaged in any way.

There is a good chance that the spark plug wiring has been dislodged after the lawn mower has been put away for an extended period of time in storage. You must fully insert the spark plug into the engine for a secure connection.

Additionally, it would help if you examined the wire connected to the spark plug and, more critically, ensure that the spark plug itself is clean. After you have completed these steps, give your lawn mower another shot at starting.

And while we’re on the topic of spark plugs, I should mention that you should change the spark plug in your lawn mower every other year. It won’t cost you more than ten dollars and will just take a few minutes of your time.

Keep Your Lawn Mower Properly Maintained

The following are some fundamental tips to assist you with maintaining your lawn mower and ensuring that it serves you well for an extended period without having any significant repairs.

Remove The Battery

It’s not a good idea to store a battery-powered auto-start lawn mower indoors in winter. To keep the battery in good condition, remove and recharge it regularly. The battery will most likely expire the following year if it is discharged for longer than six months.

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Do These Things When The Seasons Ends

As summer ends and you store your lawnmower, there are a few things to do. First, remove fuel. If you leave fuel in the mower, it will go bad, and you’ll have to start over. over, bad gas can also corrode the lawn mower’s internals.

So, simply take it out and replace it the next time you use the lawn mower.

Replace The Oil

You may want to keep a check on the oil level, depending on how often you use your lawn mower. Low engine oil can cause engine damage.

Most people forget to add engine oil to their lawn mowers, so a good habit to get into is checking the oil every time you add gas.

This simple habit will assist you in safeguarding the mower and help it run smoothly.

Regularly Clean Your Lawn Mower

Each time you use the lawnmower, you must clean it. importantly, you must make sure the lawnmower is clean and free of debris before storing it.

There is not much work involved here; just look under to see if any clumps of grass or other debris have become embedded.

Regularly Check The Air Filter

The air filter must be clean and free of any debris. The air filter should be properly cleaned if it isn’t too blocked. However, if the air filter is too dirty, you should consider getting a new one. Air filters are cheap and should be replaced annually.

It keeps the engine operating smoothly and ensures its performance.

Final Thoughts

It can be a little challenging to start the lawn mower after a time of hibernation, but with a little bit of pulling with the pull rope and a lot of cursing, you can generally get the lawn mower rolling. The best course of action is to change the gas and clean the spark plugs.

In rare circumstances, replacing the plugs entirely can be your only choice. However, nothing is more gratifying than pulling your lawnmower out of storage and having it start up without a hitch. So, make sure you store and take care of your lawn mower properly!

Frequently Asked Questions (FAQs)

Will old gas keep a lawn mower from starting?

Using old gasoline in your lawn mower can lead to a number of issues. Even though your lawnmower may still run on old gas, it might not run as smoothly. If your machine’s engine doesn’t start because of old fuel, you must clean off the built-up residue and replace the fuel.

How do you clean old gas out of a lawn mower?

One approach to get rid of the old gas is to either siphon it out with a hose or transfer it to gas can using a baster/pipette from the lawnmower’s gas tank. Once the gas has been taken out, carefully spray a carburetor cleaner into the intake hole where fuel enters the carburetor.

What happens when you put bad gas in a lawn mower?

One of the most common contributors to a lawnmower’s inability to function properly is the use of bad gas. So, if a mower isn’t working properly, you should examine the gas first. A mower with old gas may have trouble starting, idle poorly, and make odd noises.

Can I mix new gas with old gas?

It is not a good idea to combine old and new gas for a number of reasons, the most important of which are as follows: Since old gas deteriorates with time, it shouldn’t be added as it has already lost its combustible quality. Old gas can induce sputtering, and there is a chance that it will not let your lawn mower turn on at all.

Is 10-year-old gas still good?

In general, gas can be stored safely for 3 to 6 months; by adding fuel stabilizers, you may increase this time to around a year (under the right conditions, of course). So, there is no way that gas that has been sitting for ten years is still and can be used in a lawn mower.

How to Start a Lawn Mower with Old Gas: Step-By-Step

When a lawn mower hasn’t been run in a while, it may fail to start or run sluggishly like it’s going to die. Storing a lawn mower with gas for long periods can develop issues in the fuel system that have to be dealt with.

A lawn mower with old gas must be drained and filled with fresh gas. The fuel filter and fuel lines must be checked for fuel restrictions. The carburetor is likely to be the cause of a lawn mower not running due to old gas. It must be cleaned, rebuilt, or replaced to get your mower running after storing it with old gas.

Protect yourself when working on your lawn mower. This includes wearing safety glasses and working in a well-ventilated area.

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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.

How Long Can Gas Sit in a Lawn Mower?

Gas can sit in a lawn mower for up to 30 days before it begins to break down and negatively affect your lawn mower. Old gas leaves behind a varnish that will gum up the fuel system resulting in fuel restrictions and a mower that bogs down and runs sluggish.

Purchase and consume your gas within 30 days. If you have more gas than you can consume, add a fuel additive to stabilize it to make it last a little longer. Read about the right kind of gas to use in a lawn mower and how to properly store and care for it in “This is the Type of Gas Lawn Mowers Use“.

How to Start a Lawn Mower with Old or Bad Gas

Step 1: Remove the Old Gas

Old gas isn’t good for your fuel system. Most gasoline includes ethanol, an alternative fuel often made of corn, that attracts moisture to the fuel system. This ethanol and moisture mixture can leave behind gummy deposits causing fuel restrictions.

It can also separate from gasoline over time and sink to the bottom of the tank. This mixture runs hot when it burns in the cylinder potentially causing engine damage.

When you find you are running old gas in your gas tank, follow these steps to remove the old gas and fill it with fresh gas.

  • Remove the gas from the tank using a fuel siphon pump. This is a handy tool that helps extract fuel out of the tank allowing it to flow through a tube and into a fuel container.
  • Once the fuel tank is empty, fill it with fresh gasoline with a fuel additive mixed in to clean and remove moisture from the fuel system. I use Sea Foam Motor Treatment in my lawn mower. Mix according to the directions on the bottle.
  • Start and allow your mower to run until it doesn’t run sluggishly. If your mower still doesn’t start or keeps running sluggishly, continue troubleshooting and fixing the fuel components that may be have been affected by the old fuel creating fuel restrictions.

Step 2: Check for a Clogged Fuel Filter

Your fuel filter can become clogged with dirt and old fuel that has been sitting in your mower. When dirty and sticky deposits flow out of the fuel tank, the fuel filter will not allow them to pass through the filter.

The filter will become plugged which restricts the amount of fuel flowing through the fuel lines keeping your lawn mower from starting.

Replace a clogged fuel filter with a new filter. Pay attention to the arrow on the side of the filter when installing it. For correct installation, place the inline fuel filter between the fuel lines with the arrow pointed in the direction of the lawn mower’s fuel flow.

Step 3: Check for a Clogged Fuel Line

Next, move on to check for a clogged fuel line. Again, old fuel can leave sticky deposits that will restrict flow in the fuel lines on your mower. To check for good flow in the fuel lines, you’ll have to stop and start the fuel flow while checking for flow coming out of the lines using these steps:

Check fuel flow in a lawn mower fuel line

  • Stop your mower’s fuel flow by preventing fuel from flowing out of the fuel tank.
  • Use the fuel shut-off valve to turn off the fuel supply. The fuel shut-off valve is typically located near the bottom of the fuel tank. You may find it under the seat of some zero-turn lawn mowers.
  • If you don’t have a fuel shut-off valve on your model lawn mower or just can’t locate it, use fuel pinch pliers to crimp the fuel line to stop the flow.

Step 4: Check for a Dirty Carburetor

Now that you have confirmed you are getting good flow to the carburetor by first checking to make sure fuel is flowing through the fuel filter and fuel lines, it’s time to check the carburetor.

The carburetor is responsible for regulating the amount of fuel that gets mixed with air to form a combustion.

A little fuel gets stored in the carburetor bowl once it leaves the fuel tank. When the fuel is old, it can cause the fuel jet to become clogged or freeze up the small parts of the carburetor and stop functioning. The carburetor must be cleaned.

If you are somewhat mechanical and don’t mind working with small parts, you should be able to handle removing and cleaning the carburetor. Just follow these instructions I provide here to clean it.

Sometimes cleaning isn’t enough. Internal parts can become damaged and require the carburetor to be rebuilt or replaced.

You also have the option of bringing your mower to a small engine mechanic or to your lawn mower dealership to have the carburetor cleaned, rebuilt, or replaced.

Fuel Problems that Can Prevent Your Lawn Mower from Starting

Bad Fuel Pump

If you have a carburetor that sits higher than the fuel tank, you’ll need a fuel pump to work against gravity and push fuel to the carburetor. When the fuel pump fails, your lawn mower won’t start.

Once you confirm you are getting fuel to the pump, check the flow out of the pump by removing the fuel line from the carburetor and placing it in a container to collect fuel.

Start the mower and watch for a steady or pulsating flow of fuel coming out of the line. If you’re not getting good flow, replace the fuel pump.

Broke or Plugged Fuel Cap

The fuel cap can break or plug preventing it from venting sufficiently. When air isn’t able to pass through the vent, the fuel tank forms a vacuum. This vacuum prevents fuel from flowing out of the tank and getting to the engine.

Determine whether or not your cap is bad by starting and stopping the lawn mower with the fuel cap on and off.

If your mower starts with the fuel cap off, once the air is allowed into the fuel tank, but quits running after a show period after it’s installed, you most likely have a bad fuel cap. Go ahead and replace the cap.

Is it Okay to Mix Old Gas with New Gas in a Lawn Mower?

It is not okay to mix old gas with new gas in a lawn mower. Gas begins losing its combustible properties and leaves behind a varnish as soon as 30 days after purchase.

Adding new gas to old gas does not solve the problems you’ll encounter by running old gasoline. These problems include fuel restrictions causing a lawn mower to run sluggishly or not run at all.

Dispose of old gasoline in a lawn mower before filling it with fresh gasoline. Remove moisture from the fuel system by adding a fuel additive like Sea Foam to the gas.

This product not only reduces moisture, it cleans the fuel system and stabilizes the fuel so it lasts a little longer before it begins to break down.

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.

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

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Will Bad Gas Ruin A Lawn Mower: All You Must Learn About It

Imagine this: it is time to mow your grass, and your equipment is causing you issues. It won’t start, no matter the effort you put into it. But that’s weird: it is not an old mower.

But did you know that what you put on it will affect your equipment’s durability? It might never cross your mind that gasoline might spoil. But the truth is that gas does break down over time.

Just like food items spoil, fertilizers and gas might not perform as well after some time. But will old gas ruin a lawnmower? And what should you know about it?

Will Bad Gas Ruin a Lawn Mower?

Let’s go straight to the core of the question. The truth is that old gas in your lawnmower might cause it to perform poorly (or not start). Your mower might not run smoothly or sputter during operation.

The situation might worsen if your gasoline gets into contact with water: sediments building up in the tank can end up in the carburetor, which will cause trouble in starting your mower.

Don’t forget that water is denser than gasoline, so if there is some in your fuel, it will get into the carburetor, which will cause hard starting, running, and stopping.

Of course, the impact of old gas on your mower depends on the type of equipment you use. But what causes problems to your tool and why?

Over time, additives in the gasoline break down and form sediments while alcohol octane boosters (which affect the gas volatility) evaporate and leave what’s left less combustible.

Plus, inadequate storage might contribute to its degradation. Indeed, water build-up can cause it to stop performing as it should.

Also, the level of degradation depends on the product you purchase: low-quality ones might spoil in as little as 30 days. But if you properly store your gas, it might stay good for as long as one to three years. You might be able to extend its shelf life by treating it with stabilizers.

Can you Fix Your Mower?

If you are sure your mower isn’t working because you are using old gasoline, the best thing you can do to fix the problem is to remove residue that might be choking your tool’s engine.

If there is gasoline in the tank still, remove it: using the same gas after fixing your equipment will cause the same problems. When the oil you use on the engine is dirty, it grinds on parts and might ruin the mechanism.

If the oil level is low, it can even burn it! So, we suggest you not skip changing the gasoline on your mower. Don’t forget that you should do it every 25 to 50 hours of usage (or every three months: whichever comes first). Doing so will keep damage to a minimum.

If you have plenty of old gasoline that you can’t use on your mower, don’t worry: it is possible to recondition it. However, ensure you check your state’s regulations: each area has different rules.

Reconditioning involves filtering the gasoline using fabric or other fine materials and mixing it with fresh products in a set ratio. The result is only suitable for engines with carburetors. Remember not to use it in fuel injection mechanisms.

Also, depending on your mower, you might have to remove and clean the carburetor. And if the issue is so severe that the fuel line clogs, you might have to replace that too!

Will Bad Gas Ruin A Lawn Mower: The Bottom Line

So, despite what you may be thinking, gasoline expires. Its shelf life depends on how well you store it and its quality. Don’t forget that sometimes, it is worth investing a couple of dollars more on good quality if that means avoiding issues with your mower.

If you allow external elements (like water) to get into it, you might cause it to degrade sooner. Also, running small engines with old gasoline might have a considerable impact and ruin your mower so much that you won’t be able to fix it. Follow the recommendations of changing the oil in your equipment regularly to prevent that from happening.

If you need to extend your gas shelf life, purchase a fuel stabilizer: you can find that online or at your favorite gardening store. Choose a high-quality product for the best results.

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