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!

starting a lawn mower with old gas

If your mower starts stuttering and won’t start after not using it for a while, the gas in it has most likely gone bad.

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

Reconditioning Old Gas

There is a simple way to recondition old gasoline so you can use it in an emergency.

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!

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Fixing A Mower With Old Gas

Fixing A Mower With Old Gas - starting a lawn mower with old gas

Changing the gas & cleaning spark plugs is the most effective way to get a lawn mower with old gas going again.

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?

Why Is Old Gas Bad For A Lawn Mower?

Even though your lawnmower may still run on old gas, it will not run as smoothly as it should.

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?

Why Does Old Gas Goes Bad? - starting a lawn mower with old gas

Around the 30-day mark in its shelf life, gasoline begins to exhibit signs of deterioration.

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.

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Other Issues That Prevent A Mower From Starting

Other Issues That Prevent A Mower From Starting - starting a lawn mower with old gas

A bad fuel pump could also be why your lawn mower is not 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

Utilize Ethanol-Free Fuel

Gas without ethanol is more efficient than fuel with an ethanol blend.

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. 

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Avoid Flooding The Carburetor

Avoid Flooding the Carburetor

Carburetor flooding occurs when too much gas enters the carburetor and flows out the throttle shaft or vent tube.

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?

How To Start A Lawn Mower With Old Gas

Dust and old gasoline can clog your mower’s fuel filter and prevent it from starting.

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

Keep Your Lawn Mower Properly Maintained - starting a lawn mower with old gas

Keep your lawn mower well-maintained. It will increase its life and keep it working at its best!

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.

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. Moreover, 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. More 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.

Sources For Further Reading

Lawn Mower Safety. (2022). West Virginia University. Retrieved 11 September 2022, from

Lawn Mower Safety. (2022). The University of Utah. Retrieved 11 September 2022, from

Guidelines for Mowing Lawns Properly – Lawn Talk- University of Illinois Extension. (2022). Retrieved 11 September 2022, from

No Lawn Mowers Needed in… | University of Northwestern, St. Paul. (2022). Retrieved 11 September 2022, from

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