Bad Gas in Your Lawn Mower? What To Do!

The smell of freshly cut grass, the gentle hum of the engine, and the satisfaction of a well-maintained lawn – it’s all part of the joy of owning a lawn mower. But this idyllic picture can quickly turn sour when your trusty mower sputters and coughs, refusing to start. The culprit? More often than not, it’s bad gas. This article will dive into the problem of bad gas in your lawn mower, explaining why it happens, how to identify it, and most importantly, how to fix it. You’ll learn how to troubleshoot, clean, and ultimately get your mower running smoothly again.

What is bad gas?

Gasoline, unlike wine, doesn’t age gracefully. Over time, it deteriorates. The chemicals in gasoline break down, leading to gum, varnish, and other deposits that clog fuel lines, carburetors, and fuel filters. This can cause a variety of problems with your lawn mower, from difficulty starting to complete engine failure.

Identifying Bad Gas

The first step to fixing your lawn mower is identifying the problem. If you suspect bad gas, here’s how to check:

1. Check the Smell

Bad gas has a distinct, almost pungent smell, quite different from fresh gasoline. If you smell something off when you open your fuel tank, it’s a strong indicator of bad gas.

2. Look at the Gas

If the gasoline in your tank is old or has been exposed to extreme temperatures, it might have changed color or texture. Fresh gasoline is typically clear, while old gas can become cloudy, discolored, or even have a gummy residue at the bottom of the tank.

3. Observe Your Mower’s Behavior

If your lawn mower has trouble starting, runs unevenly, or stalls frequently, bad gas could be the culprit.

Troubleshooting Your Mower

Once you’ve identified bad gas, you need to address it. Here’s a step-by-step guide:

1. Empty the Gas Tank

The most effective solution is to completely empty the tank of bad gas.

Safety First:

  • Always work in a well-ventilated area, preferably outdoors.
  • Wear safety glasses and gloves to protect yourself from spills and fumes.
  • Never work near open flames or sparks.

Emptying the Tank:

  • Disconnect the spark plug wire to prevent accidental starting.
  • Carefully remove the fuel cap and pour the bad gas into a suitable container, like a gas can.
  • Dispose of the bad gas properly. You can contact your local waste management facility for disposal options.

2. Clean the Fuel System

Once the tank is empty, it’s time to clean the fuel system. This is essential to remove any remaining deposits and ensure smooth fuel flow.

Cleaning the Fuel Lines:

  • Remove the fuel lines: Disconnect the fuel lines from the fuel tank and carburetor.
  • Clean the lines: Use a fuel line cleaner or compressed air to blow out any debris or deposits inside the lines.
  • Reinstall the fuel lines: Connect the fuel lines back to the fuel tank and carburetor.

Cleaning the Carburetor:

  • Remove the carburetor: Depending on your mower model, you may need to consult your owner’s manual for specific instructions.
  • Disassemble and clean: Disassemble the carburetor and use a carburetor cleaner to remove any deposits.
  • Reassemble and reinstall: Reassemble the carburetor carefully and reinstall it on the mower.

Cleaning the Fuel Filter:

  • Locate the fuel filter: It’s usually located near the fuel tank or carburetor.
  • Remove and inspect: If it’s reusable, clean it with a fuel filter cleaner. If it’s disposable, replace it with a new one.

3. Fill with Fresh Gas

After cleaning the fuel system, fill the tank with fresh, high-quality gasoline.

Fuel Quality Matters:

  • Use fresh gasoline: Avoid using gasoline that’s been sitting in a gas can for more than a month.
  • Use the recommended fuel type: Check your owner’s manual for the recommended fuel type and octane rating for your mower.
  • Add fuel stabilizer: This helps to prevent gasoline from deteriorating over time, especially if you won’t be using your mower for an extended period.

4. Start and Test Your Mower

Now, reconnect the spark plug wire and try to start your mower. If it runs smoothly, you’ve successfully dealt with the bad gas.

Preventing Future Bad Gas Issues

Once you’ve dealt with the bad gas problem, it’s essential to prevent it from happening again. Here are some tips:

  • Use fuel stabilizer: Add fuel stabilizer to your gas tank, especially if you won’t be using your mower for a while. This will help to extend the shelf life of the gasoline.
  • Empty the tank for extended storage: If you plan to store your mower for several months, it’s best to empty the tank completely and run the engine until it stalls to clear any fuel from the lines.
  • Use fresh gas: Always use fresh gasoline for your mower. Don’t use old or stale gas.


Bad gas can be a frustrating problem for lawn mower owners, but it’s usually an easy fix. By understanding the causes, identifying the problem, and following the troubleshooting steps outlined in this article, you can get your mower running smoothly again. Remember, regular maintenance and preventative measures are crucial for preventing future bad gas issues and keeping your mower in top shape for years to come. With a little care and attention, you’ll be able to enjoy the satisfaction of a well-maintained lawn and the gentle hum of your mower’s engine for many seasons to come.

Frequently Asked Questions

1. How can I tell if my lawn mower has bad gas?

The most noticeable sign of bad gas is a difficulty starting your lawn mower. If your mower starts and then immediately dies, or if it takes a long time to start and runs poorly, it’s likely due to old gas. Other signs include a musty or sour smell coming from the fuel tank, a milky or cloudy appearance to the gasoline, and visible sediment at the bottom of the tank.

If you suspect bad gas, it’s best to drain the tank and replace it with fresh fuel. Additionally, check for any signs of corrosion or damage in the fuel system caused by the old gasoline.

2. What happens if I use bad gas in my lawn mower?

Using old gas in your lawn mower can lead to a variety of problems. It can clog your carburetor, leading to poor engine performance and difficult starting. Bad gas can also damage other components in your fuel system, such as the fuel lines and the fuel pump. This can result in costly repairs or even a complete engine failure.

The best way to avoid these problems is to use fresh gasoline and store it properly to prevent it from going bad. Consider using a fuel stabilizer to extend the shelf life of the gasoline.

3. How long does gasoline stay good for?

Gasoline starts to degrade after about 30 days, and it will continue to deteriorate over time. The rate of degradation can be affected by factors such as temperature, humidity, and the presence of contaminants.

To ensure your gasoline stays fresh, it’s recommended to use it within 30 days. If you need to store gasoline for longer periods, use a fuel stabilizer and store it in a cool, dry place.

4. Can I use bad gas in my lawn mower if I mix it with fresh gas?

While adding fresh gas to bad gas might seem like a solution, it’s not recommended. The old gasoline can still contain contaminants and residues that can damage your lawn mower’s engine.

It’s best to drain the old gas completely and refill the tank with fresh gasoline. This will ensure that your mower runs smoothly and prevents potential damage to your engine.

5. How do I drain the gas from my lawn mower?

Draining the gas from your lawn mower is a simple process. First, locate the fuel valve and turn it to the “off” position. Next, place a container under the fuel tank drain valve and open the valve to let the gasoline flow out.

Once the tank is empty, close the valve and dispose of the old gasoline properly. Never pour gasoline down the drain, as it can contaminate the water supply.

6. What should I do if my lawn mower won’t start after using bad gas?

If your lawn mower won’t start after using bad gas, it’s likely that the carburetor is clogged. To clean the carburetor, you can either disassemble it and clean it manually, or use a carburetor cleaner.

You can also try using a fuel line cleaner to help remove any remaining contaminants in the fuel system. If these steps don’t resolve the issue, it may be necessary to take your lawn mower to a qualified mechanic for repairs.

7. How can I prevent bad gas in my lawn mower?

The best way to prevent bad gas in your lawn mower is to use fresh gasoline and store it properly. When storing gasoline, use a fuel stabilizer to extend its shelf life. Additionally, ensure that your fuel tank is sealed tightly to prevent evaporation and moisture from entering.

Always check the expiration date on the gasoline container before using it and consider using a fuel additive to further improve the quality and performance of your gasoline.

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