Gas Coming Out Of My Lawn Mower Exhaust – What’s Wrong?

You were driving around the yard mowing the lawn and suddenly you see gas coming out of the exhaust. This could be a serious issue, especially if it catches a spark. We have researched this issue in-depth and found some simple DIY methods that can help you repair your lawn mower without having to take it to a mechanic.

Gas leaking in your lawn mower's exhaust muffler could be a sign of any or a combination of the following issues in the carburetor:

1. Stuck/warped carburetor float  

2. Rusty carburetor needle

3. Worn carburetor needle seat

A gas leak coming from the lawn mower exhaust is never fun, but it's also not difficult to fix. Keep on reading to learn more about how to deal with a lawn mower exhaust leak. 

Exploit, old lawn mower and the cloud of exhaust fumes, Gas Coming Out Of My Lawn Mower Exhaust - What's Wrong?

Carburetor Issues That Cause Lawn Mower Exhaust To Leak Gas

Before you think of replacing your lawn mower's carburetor, it might help to understand the mechanisms behind a carburetor.

What Is A Carburetor?

A carburetor is a device that mixes fuel and air together to create an engine's power. The gas mixture is then ignited by the spark plug to create the explosion needed for the engine to work.

Carburetors are very sensitive devices that require regular maintenance. They use a fine mesh screen called the “jet” to atomize gasoline into tiny droplets.

One of the most common causes of a carburetor malfunction is dirt. Dirt can clog the jets, restricting the amount of fuel that flows through.

If the mesh becomes clogged with dirt, the fuel will not be dispersed properly, and the air-to-fuel ratio can get out of whack. This will result in sluggish engine performance and inefficiency in terms of fuel consumption.

In some cases, a clogged carburetor that does not undergo periodic cleaning and maintenance may cause the engine to suffer permanent damage.

Elements of the fuel system of a gasoline trimmer. Carburetor Mower machine in hand.

What Is A Carburetor Float?

A carburetor float regulates the amount of fuel that is supplied to the engine by opening or closing the throttle valve in the carburetor. The float is typically attached to a float lever which acts on the throttle valve in the carburetor.

A spring keeps the float closed. If the engine requires more fuel, the float is moved to open the throttle valve, allowing more fuel to enter the carburetor. If the engine needs less fuel, the float is moved to close the throttle valve, causing less fuel to enter the carburetor.

What Happens If Carburetor Float Is Stuck/Warped?

A carburetor float works in the same way as the float in your toilet flush system does. So just imagine what will happen to your toilet if the float is stuck in the open position.

Similarly, if the float in your carburetor is stuck, fuel will flow out of it. A worn float spring is most likely the culprit for this issue. The float spring allows the float to go up and down as the latter meters out the fuel to the engine. 

On the other hand, the float pin is what holds the float spring, the float itself, and the carburetor together and is different from the carburetor needle.

Carburetor floats are usually made of plastic material that is heat resistant. If the float has no issues staying closed or open, then it's most likely leaking fuel because it is warped or damaged. 

Carburetor Needle And Seat: A Basic Valve

The carburetor needle is a part that regulates the flow of fuel. It is responsible for varying the amount of fuel entering the engine to match the needs of the engine.

It is essential to ensure that the needle seat and the needle are in place in order to maintain the functioning of your carburetor. A properly installed needle seat is vital for ensuring that the engine runs smoothly and efficiently.

If either the needle or needle seat becomes damaged or clogged, it may affect the fuel mixture, leading to fuel leaks and other issues like sputtering or engine misfiring.

The video below keeps this topic sweet and simple, so check it out.

How To Fix Fuel Leaking From Lawn Mower Exhaust

Man cleaning lawn mower.

There’s nothing worse than finding that your lawn mower is leaking fuel in the spot where you least expect it: the muffler. However, you may be surprised to learn that there are a few easy ways to fix this problem before it gets really bad. 

Here are the steps to follow to fix a leaking fuel in the lawn mower muffler:

1. Drain the oil

This is to prepare the lawn mower for the carburetor cleaner. Make sure to drain all of the oil from the mower as best as you can.

You should do this because if the oil is contaminated with dirt or metal shavings, chances are these particles could get stuck into the carburetor and aggravate the issue. So drain the oil as much as possible.

2. Apply carburetor cleaner

The second step is to use a carburetor cleaner. Carburetor cleaners usually consist of a solvent that dissolves and breaks the bond of the sticky, gooey deposits that can gum up and jam the float.

Carburetors are complex pieces of machinery. It is easy for dirt and metal shavings to find their way into the carburetor and clog it. 

Check out this carburetor cleaner on Amazon

3. Run the lawn mower

Turn on the engine and let the lawn mower run until the carburetor cleaner has completely traversed every nook and cranny of the carburetor.

The video below shows every step in this process:

If after applying the carburetor cleaner the leak still does not stop, chances are there is some other blockage in the carburetor. In this case, you might want to remove the carburetor and check what is causing the problem.

Alternatively, you may also choose to have the entire carburetor assembly replaced if you find issues that are not related to clogging or rusting with any of its parts. This saves you time and is more cost-efficient than replacing defective parts.

Can You Spray Carburetor Cleaner Directly Into The Lawn Mower Carburetor?

Lawn mowers have carburetors that require cleaning to make sure that they operate properly. Most of us think that we should only use liquid carburetor cleaners in the same way we change and refill engine oil during routine maintenance.

However, there is a better way to clean a carburetor that you may not be aware of, and this is to spray it directly into the carburetor with the engine running.

Can Brake Cleaners Be Used As Alternatives For Carburetor Cleaners?

Lawn mower.

A brake cleaner is the next best alternative to a carburetor cleaner, and it offers the same benefits. 

A brake cleaner is used to restore the performance of the brakes on your car. The cleaner helps to clean the carbon deposits off your brakes, making them work better. This is the reason why brake cleaners are safe to use as an alternative in case carburetor cleaners are out of stock.

Check out this brake cleaner on Amazon

Is Alcohol Effective In Cleaning Carburetors?

Alcohol is used in a lot of different ways and is usually very effective at what it does. But cleaning your lawn mower carburetor with it is probably one of the worst things you can do to it. Alcohol can corrode some parts of your carburetor that are made of aluminum and zinc, so it's best to avoid it.

Can You Use Vinegar In Cleaning Carburetors?

Most homeowners think of vinegar as a great way to clean a lot of things around the house. But vinegar contains a chemical called acetic acid, which can react with certain types of alloys and metals. The downside to using vinegar is that it has an acidic quality that makes it corrosive to metal.

Acetic acid can also cause rust to form on metal surfaces. This can leave rust marks not only on your lawn mower carburetor, but on your car, boat, and motorcycle. 

Is It Safe To Leave Gas In Your Lawn Mower Over The Winter?

It’s a good idea to remove the fuel from your lawnmower during the winter months. Leaving the gas in the tank can lead to several problems, including a potential clogging in the carburetor and in the fuel filter when reusing the same fuel after winter.

Gasoline crystallizes at a certain temperature and these gas crystals could get into the fuel filter and clog it. In addition, gasoline is made up of many different chemical compounds.

It can break down over time. This leads to the formation of gummy residue, which coats the engine and creates a sticky mess. To avoid this problem, do not leave gasoline in a mower for extended periods of time.

How Long Should Gasoline Be Allowed To Sit In Lawn Mower Fuel Tank?

Lawn mower at work

As mentioned above, gasoline can break down if left sitting in the gas tank for an extended period of time. That’s why it is recommended that gasoline should be changed every 30 days.

If you store your lawn mower in the garage, you can easily accomplish this by either emptying the tank or adding a stabilizing agent. A fuel stabilizer is a mixture of chemicals that can prolong the shelf life of gas by neutralizing harmful components. 

Check out this fuel stabilizer on Amazon

In Closing

Leaks in lawn mowers come in many different ways. Gas leaking from your lawn mower's exhaust muffler is usually a sign of a carburetor issue.

While you should always get a professional to do a thorough inspection of your lawn mower, most leaks can be easily fixed if you are willing to try. With a little patience and attention to detail, you can repair these issues before they become major problems.

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