9 Reasons Your Lawn Mower Is Leaking Gas(+Quick Fix)

It is common for lawn mowers to have gas leakage 1-2 times. However, seeing the gas puddles and strong smell from your garden is quite frustrating. This article will explain the reasons behind the leakage. 

A lawn mower leaks gas due to stuck float and float needles, broken fuel lines, tanks, valves, filters, and pumps, poor gas caps, bad primer bulbs, and carburetor issues. Since there can be numerous reasons, you must find the right one and solve it quickly to fix the leakage. 

This article will explain the signs of leakage, a few major reasons behind gas leakage, and how to solve them. Some reasons may not pertain to the mower you own, but it is good to know all the causes in case you face them. 

lawn mower fuel filter

Signs your lawn mower is leaking gas.

Sometimes, the gas dissipates, and you remain unaware of the problem. 

So, your mower will show some significant signs of leakage, for example:

  • Strong gas odors
  • Dead grass spots in the lawn after a few days of mowing. 

Why does your lawn mower leak gas?

There are several reasons behind a lawn mower leaking gas. 

This section will emphasize the major grounds and how to troubleshoot them:

Carburetor bowl issues 

The carburetor is where the gas is stored after it leaves the fuel tank. 

It is the place where the gas mainly leaks first. 

First, you should examine the bottom of the carb. 

This place is called the bowl. 

A thin o-ring resembling a rubber band will go between the carb base and the bowl. 

A carburetor bowl is a common place for gas leakage. 

The area becomes hot when the mower is in use and cools down when the mower is shut off. 

As a result, the o-ring will constantly transfer from hot to cold temperatures. 

These temperature changes can put a strain on the ring.

The stress on the o-ring will harden the ring and make it lose its strength to seal. 

How to fix it?

You should replace the rubber gasket at the bowl’s bottom. 

Here are the steps to replace the gasket:

  • Shut off the fuel supply to the mower.
  • Unscrew the screw and drop the bowl.
  • Replace the gasket, put the bowl back into the mower, and screw it. 
  • Turn the fuel on and wipe the carburetor bowl to ensure no more leakage. 

Stuck float

Lawn mower engine repair 2

Check the carburetor opening. 

The float will be stuck if there is a fuel leak from the air intake port.

The float helps regulate the amount of gas stored inside the bowl. 

It turns the gas on and off. 

When the float gets stuck, the gas will not shut off. 

As a result, the fuel will run out of the carb. 

When this happens, tank the carburetor apart and check the reason behind the stuck float. 

How to fix the stuck float?

Based on the reason behind the stuck float, you may have to clean, rebuild, or replace it. 

To replace the float:

  • Remove the engine cover and the bolts. 
  • Pull the spark plug cable and take it out. 
  • Remove the belt securing the air filter cover and the filter by unscrewing it in the filter base. 
  • Clamp the fuel line to the carburetor. 
  • Detach the spring clip from the fuel line to the carburetor. 
  • Lift the tank, remove the throttle and choke linkages, and pull the carburetor from the engine. 
  • Remove the fuel bowl and bolts. 
  • Extract the pins holding the float and lift out the float and the needle. 
  • Detach the needle and attach it to the new float. 
  • Place the needle and the float back in place and install the pin. 
  • Reattach all the components back in place – the fuel bowl, the carburetor, the throttle and choke linkages, the fuel tank and line, the spring clip, the filters, and the filter covers. 
  • Reposition the engine cover and secure it and connect the spark plug. 

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Stuck float needle

Once you check the float and find out that the float is not the problem, the problem could be in the needle. 

The float needle can also get stuck and keeps the gas flowing to the bowl with the float. 

How to fix the stuck needle?

You can use a hammer and slightly hit the sides of the carburetor to free the needle. 

Follow the steps discussed in the float to see the needle. 

Hitting can work once or twice, but you need to open the carb apart to check the needle’s condition and rebuild the carburetor. 

Fuel lines

Check the fuel lines coming out of the fuel tank. 

If the lines are dry-rotted or cracked, you should replace them. Such lines are responsible for leaking gas. 

Most fuel lines are damaged due to aging. 

These lines do not have tight seals around the carburetor fittings, tanks, or filters when they get hard. 

As a result, the gas will leak. 

How to fix the gas lines?

Before repairing or replacing the fuel lines, drain the remaining fuel left in the tank. 

Use a plier to remove the fuel line clamp and pull it from the fitting. 

You can rotate the fitting, too, if pulling does not work. 

Now remove the damaged line, and install a new fuel line that matches the size of the old one. 

After installing the line, replace the clamp. Lubricate the line for easy sliding into the fitting. 

Fuel tank 

Lawn mower gas refill

A damaged fuel tank is another reason behind gas leakage. 

When your lawn mower faces an accident, the fuel tank somehow cracks. 

Accidents include heating the tank against the low-hanging shrubs or something falling over the tank. 

Besides accidents, your fuel tank will crack due to corrosion and rust when your lawn mower ages. 

You need to check the rust holes in the tank for confirmation. 

If you have a plastic fuel tank, the seams at the molded plastic can get separated and lead to gas leakage. 

How to fix the fuel tank?

Replacing the tank is the only way out. 

Some tanks are easy to remove and replace as they are in separate pieces. 

But others under the engine shroud make removal difficult. 

No matter the location, you must replace it after you empty the tank. 

If the fuel tank is a separate piece, remove the fuel line from the tank and separate it from the mower. 

If the tank is under the engine shroud, remove the shroud first. 

In some models, you need to remove the starter assembly first. 

After removing the shroud, detach the fuel line and dismount the tank. 

Replace the tank with a new one and place everything back in place. 

Fuel filter

lawn mower fuel filter

Consider checking the fuel filter when your lawn mower leaks gas. 

There are chances of gas leakage due to the dirty filters. 

The plastic inline filters start breaking down and become weak and soft after holding gasoline for a very long time. 

Sometimes, the ends of the filters will collide when you try to open them. 

The main cause of the soft and melted filter is bad gasoline. 

What to do with the fuel filters?

So, you should remove and replace the fuel filters every 3-4 months to prevent leakage. 

It is better to use recreational fuel for your lawn mowers. It is pleasant for the fuel filters. 

Fuel pump

Similar to plastic fuel filters, the fuel pump can also break down due to the bad fuel type. 

Most lawn mowers have plastic fuel pumps that deteriorate after holding the fuel for a long time. 

The gas remains on the pump for several years and begins to rot from the inside. 

The diaphragm will start leaking, and the seams of the pump will leak gas.

How to fix the issue?

You must change the pump regularly and use good-quality fuel to keep the pump from degrading.

Bad gas cap

A bad gas cap can also lead to gas leakage. 

Check the gas cap to make sure it is venting and sealed properly. 

If the venting and sealing are improper, the gas splashes around the fuel tank when you use the lawn mower. 

The gas will leak from the top of the tank, where the cap has secured it. 

Check the cap once if you are constantly smelling gas but cannot detect the source. 

The gas will dissipate before you get to see it. 

You can shake the mower to identify the problem. After shaking, the fuel will splash and wet the cap area. 

How to fix it?

You need to replace the gas cap with a new one. 

However, a new cap won’t help if you have overfilled your fuel tank. 

Primer bulb

Some lawn mowers have a primer bulb on the side of the air filters. 

The bulb can leak fuel when the bulb gets filled with fuel. You will constantly smell the gas from the mower. 

Except for overfilling, you will get a gas smell when the primer bulb connects to the fuel liner and becomes weak and brittle over time. 

Generally, rats and mice are responsible for it because they love chewing the primer bulbs. 

How to repair the primer bulb?

To fix the problem, you should remove the retaining ring of the bulb and install a new one. 

Primer bulbs can come in various designs and be attached to the mower differently. 

Most designs are attached to the mower’s side and help prime the engine during cold starts. 

To replace the bulb, remove the old primer bulb by removing the washer. 

If you have a clipped-on primer bulb, like in the Briggs & Stratton mowers:

  • Push the clip inside and slide the primer with the help of a screwdriver. 
  • For Briggs & Stratton engines, you will get a special tool for this purpose, making bulb installation easier.

If you have mowers with metal washers, like Tecumseh mowers:

  • Use a hook to pull out the washer and then the rubber primer. 
  • Fit the local tooth washer into the circular groove. 
  • Get a socket in the socket wrench having the same size as the washer. 
  • Place the socket on the washer and tap it with a hammer. 

Why should we take immediate steps about gas leakage?

Lawn mower gas

Gas leaking from the lawn mower should be immediately addressed. 

Since gas is a flammable material, letting the problem stay can lead to several issues. 

  • The gasoline leaked from the lawn mower will kill all the grass, plants, and shrubs in your garden. 
  • It can also contaminate the soil and make it impossible for new plants to grow or remain healthy. 
  • The gas can dissipate after some time, and you won’t understand the issue. As a result, your lawn can catch fire accidentally and cause serious damage and bodily harm. 

Due to these reasons, you must address the issue immediately after identifying it. 

A strong gas odor is one of the most common signs of leakage. 

Final words

Every lawn mower will experience a gas leakage issue at some point. So, you need to be careful and fix the problem immediately. The major reasons include the carburetor’s o-ring degradation, stuck float, and float needle, damaged fuel lines, pumps, filters, and tanks, a bad gas cap, and a damaged primer bulb. 

Since there are multiple reasons, you should confirm the problem before troubleshooting them.

Since we have already covered everything in this article, you can use the information provided to find out the cause of the leakage and how to resolve it. 

Also read:

Why does the lawn mower leak oil from the air filter?

One common reason behind a leaky lawn mower is excessive oil in the engine. Another reason could be that the mower has been on its side.

Will the lawn mower’s fuel line break?

Lawnmowers come with different fuel lines. Some of them can break by snagging on something like a shrub. You should replace the fuel line to prevent oil or gas leakage.

Reference: Lawn Mower Technology, Lawn Mower SafetyLawn MowingLawn CareMowing your lawn.


Hello everyone, My name is Richa and I am here to make you a better gardener by creating an in-depth and helpful resource for all the fellow gardeners out there. If I could help even a few people understand their plants better then I call it a success for my efforts.

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