Is Your Lawn Mower Stuttering? How to Clean Old Gas Out of Your Lawn Mower?

The first warm days of spring bring with them the promise of manicured lawns and outdoor fun. But for many, that promise is quickly dashed when their trusty lawnmower sputters to life, coughs, and dies. The culprit? Often, it’s old gasoline, sitting dormant in the tank, gumming up the engine and preventing it from running smoothly. This article will guide you through the process of cleaning out old gas from your lawnmower, ensuring a smooth start for a season of mowing bliss.

The key to cleaning old gas out of your lawnmower lies in a combination of draining the old fuel, cleaning the carburetor, and potentially using a fuel stabilizer for future storage.

Understanding the Problem: Why Does Old Gas Cause Issues?

Gasoline is a volatile substance that begins to degrade over time. The chemicals within it break down, forming gums and varnishes that can clog the intricate passages of your lawnmower’s carburetor. These deposits prevent the proper flow of fuel and air into the engine, leading to:

  • Difficulty Starting: The engine may struggle to ignite, or sputter and stall.
  • Poor Performance: The engine runs rough, with reduced power and uneven speeds.
  • Engine Damage: Severe gumming can lead to damaged carburetor parts, requiring expensive repairs.

How to Clean Old Gas Out of Your Lawn Mower: A Step-by-Step Guide

Cleaning old gas out of your lawnmower requires a few simple steps that can be done with basic tools and a little time.

1. Drain the Old Fuel

Before you start, gather the following:

  • A fuel container: Choose a container that’s specifically designed for storing gasoline and has a secure lid.
  • Gloves: Protect your hands from the fumes and potential spills.
  • Eye protection: Goggles or safety glasses will shield your eyes from accidental splashes.
  • A fuel filter: This is optional but highly recommended, especially if you plan to use the drained fuel for another purpose.

Safety First:

  • Work in a well-ventilated area: Gasoline fumes are flammable and can be harmful if inhaled in large quantities.
  • Never smoke near gasoline: Always ensure there are no ignition sources present.
  • Do not drain fuel near open flames or heat sources: This can cause a fire hazard.

Steps for Draining the Fuel:

  1. Turn off the engine: Ensure the engine is completely off and cold before starting.
  2. Locate the fuel valve: The fuel valve is typically located on the side or bottom of the fuel tank.
  3. Open the fuel valve: This allows fuel to drain from the tank.
  4. Place the container under the valve: Carefully position your container to collect the fuel.
  5. Let the fuel drain: Allow the fuel to drain completely until no more comes out.
  6. Close the fuel valve: Once the tank is empty, close the fuel valve tightly.

2. Clean the Carburetor

This step involves removing the carburetor from the engine and cleaning it thoroughly to remove the fuel deposits.

Tools You Will Need:

  • Carburetor cleaner: This specialized cleaner is designed to dissolve gum and varnish.
  • A small brush: A soft-bristled brush can help remove stubborn deposits.
  • Compressed air: This will help blow out any remaining debris.
  • Shop towels: For wiping surfaces and cleaning tools.

Cleaning the Carburetor:

  1. Disassemble the carburetor: Refer to your lawnmower’s manual for specific instructions on disassembling the carburetor. Generally, you’ll need to remove the air filter, fuel lines, and carburetor bowl.
  2. Clean the carburetor parts: Soak the carburetor parts in carburetor cleaner, following the instructions on the bottle.
  3. Scrub stubborn deposits: Use a small brush to remove any remaining deposits, especially around the jets and passages.
  4. Rinse the parts: Rinse the carburetor parts thoroughly with clean water to remove all traces of the cleaner.
  5. Dry the parts: Allow the parts to air dry completely before reassembling.
  6. Reassemble the carburetor: Ensure that all parts are correctly installed and secured.

3. Test the Engine

After cleaning the carburetor, it’s crucial to test the engine to ensure it runs smoothly.

Testing Your Engine:

  1. Reinstall the carburetor: Once you’ve reassembled the carburetor, reinstall it on the engine.
  2. Reconnect the fuel line: Make sure the fuel line is securely connected to the carburetor.
  3. Start the engine: Follow the manufacturer’s instructions for starting the engine.
  4. Check for smooth running: Observe the engine for any signs of stuttering, sputtering, or uneven running. If you notice any issues, double-check your cleaning process and repeat if necessary.

4. Prevent Future Fuel Issues

To avoid future fuel problems, consider using a fuel stabilizer. This additive helps prevent fuel degradation and ensures your lawnmower starts smoothly even after a long period of storage.

Using a Fuel Stabilizer:

  1. Choose a reputable brand: Opt for a high-quality fuel stabilizer designed for small engines.
  2. Follow the instructions: The instructions on the bottle will specify the correct amount to add to your fuel.
  3. Add the stabilizer to the fuel tank: Mix the stabilizer thoroughly into the fuel before storing the mower.
  4. Store the mower properly: Store your lawnmower in a cool, dry place.


Cleaning old gas from your lawnmower is a relatively simple process that can save you time and money in the long run. By following the steps outlined in this article, you can ensure your lawnmower runs smoothly and efficiently, ready to tackle your lawn care tasks with ease. Remember to prioritize safety, work in a well-ventilated area, and always refer to your lawnmower’s manual for specific instructions and warnings. With a little care and attention, you can keep your lawnmower running smoothly, year after year.


Why is my lawn mower sputtering?

There are several reasons why your lawn mower might be sputtering. The most common culprit is old, stale gasoline. Gasoline degrades over time, losing its volatility and making it difficult to ignite properly. This can lead to sputtering and other performance issues. Other potential causes include a clogged fuel filter, dirty carburetor, or a problem with the spark plug.

To determine the exact cause of the sputtering, it’s important to inspect the fuel system and other components. Check the fuel filter for any blockages and inspect the carburetor for dirt or debris. You can also try cleaning or replacing the spark plug to see if that resolves the issue.

How do I know if my lawn mower has old gas?

Old gas will look and smell different than fresh gas. It will likely have a darker color and a more pungent odor. You can also tell by the time it’s been sitting in the tank. If it’s been more than a few months, it’s likely old and should be drained.

It’s important to note that gasoline can start to degrade even within a few weeks, especially in hot weather. This is why it’s best to use fresh gas whenever possible and to avoid letting it sit in the tank for extended periods.

Can I just add fresh gas to my lawn mower?

It’s not recommended to just add fresh gas to old gas in your lawn mower. The old gas may have already started to gum up the fuel system, and adding fresh gas won’t necessarily solve the problem. It’s better to drain the old gas and refill the tank with fresh fuel.

Draining the old gas is a simple process that can save you a lot of trouble in the long run. You’ll need a container to collect the gas and a siphon hose. Be sure to drain the gas in a well-ventilated area, away from any open flames.

What is the best way to clean old gas out of my lawn mower?

The best way to clean old gas out of your lawn mower is to completely drain the fuel tank and carburetor. You’ll need a siphon hose or a pump to remove the gas from the tank. Once the tank is empty, you can remove the carburetor and clean it thoroughly with a carburetor cleaner.

After cleaning the carburetor, be sure to reinstall it properly and reassemble the fuel system. Once everything is back in place, start the engine and let it run for a few minutes to make sure the fuel system is clear of any remaining debris.

How often should I drain my lawn mower’s gas tank?

It’s a good idea to drain your lawn mower’s gas tank every few months, or at the end of the season if you won’t be using it for a while. This will help to prevent the gas from degrading and causing problems.

If you’re only using your lawn mower occasionally, it’s best to drain the tank after each use. This will ensure that the gas in the tank is always fresh and won’t have a chance to degrade.

Can I use fuel stabilizer in my lawn mower?

Yes, you can use fuel stabilizer in your lawn mower to help prevent the gas from degrading. Fuel stabilizer is a chemical that helps to prevent the formation of gums and varnish in the fuel system.

You can add fuel stabilizer to your lawn mower’s gas tank before storing it for the winter. Be sure to follow the instructions on the product label.

What are some other tips for keeping my lawn mower running smoothly?

In addition to cleaning the fuel system, there are other things you can do to keep your lawn mower running smoothly. Be sure to change the oil regularly and keep the air filter clean. You should also inspect the spark plug and replace it if necessary.

Regular maintenance will help to ensure that your lawn mower runs efficiently and reliably. If you’re not comfortable performing these tasks yourself, you can take your lawn mower to a qualified mechanic for servicing.

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