What do I do if I put bad gas in my lawn mower?

Putting bad or old gasoline in your lawn mower can cause a number of issues, from poor engine performance to complete failure. Thankfully, with some quick action, you may be able to get your mower running properly again. Here are some steps to take if you accidentally use bad gas in your lawn mower:

Step 1: Stop Using the Lawn Mower Immediately

As soon as you realize you’ve put bad gas in the mower, stop using it. Running the engine with contaminated fuel can cause further damage. The longer you operate the mower, the more gas gets pulled into the carburetor and combustion chambers, spreading the bad fuel throughout the system.

Step 2: Drain the Old Gasoline

The next step is to fully drain the old, contaminated gasoline from the fuel tank, fuel lines, and carburetor. This will remove most of the bad gas from the mower’s fuel system.

To drain the tank, locate the fuel shut-off valve and turn it to the “off” position. Then locate the fuel drain bolt or valve at the bottom of the tank. Place a container under the mower to catch the drained gas. Open the drain bolt/valve and allow all gasoline to drain out. Make sure to wear protective gloves when handling gasoline.

For the fuel lines, disconnect them from the carburetor and fuel filter and aim them into your drain container. Blow out the fuel lines with compressed air if possible. Doing this will force out any remaining bad gas.

Finally, drain the carburetor by loosening the bowl bolt on the bottom. Gasoline will drain out once the bolt is removed. Make sure to catch the drained fuel in your container.

Step 3: Add Fresh Gasoline

With the old gasoline fully drained, you can now add fresh, high-quality gas to your mower’s fuel system. Use only gas that has been purchased recently from a busy gas station, preferably one with ethanol-free gasoline if your mower requires it. This fresh fuel will flush out any remaining traces of bad gas still left behind.

Slowly add the new gasoline to the fuel tank, taking care not to overfill. Reconnect the fuel lines to the carburetor and fuel filter. Tighten the carburetor bowl bolt to secure it back in place. Turn the fuel shut-off valve back to the “on” position.

Step 4: Clean or Replace the Carburetor Filter

The carburetor filter prevents debris and contaminants from entering the carb. But over time, this filter can become clogged from bad gasoline. Remove the carb filter and inspect it. If it appears clean, simply reinstall it. If there is visible debris, try rinsing it with carburetor cleaner fluid. You may need to purchase a replacement filter if it is overly dirty.

Step 5: Add Fuel Stabilizer

Once you have fresh gasoline in the mower, also add fuel stabilizer to the tank. Fuel stabilizers prevent gasoline from deteriorating for up to 2 years when stored. This will prevent any future issues with bad gas if the mower sits unused for a period of time.

Always use fuel stabilizer products as directed. Most recommending adding 1 oz of stabilizer per gallon of gasoline. Shake the fuel tank after adding to fully mix the stabilizer throughout the fuel.

Step 6: Attempt to Start the Mower

With fresh gasoline treated with stabilizer now in the tank, try starting the mower’s engine. If it starts up and runs normally, the bad fuel has likely been fully removed from the system. Let the mower run for 10-15 minutes to cycle the fresh gas through.

If the engine struggles to start or fails to start at all, further cleaning is needed. Proceed to the advanced steps below.

Advanced Steps for Severe Fuel Contamination

If the previous steps did not get your mower running properly again, more intensive cleaning is required:

Run a Fuel System Cleaner Through

Specialized fuel system cleaners can help dissolve and remove fuel deposits and residue. Add fuel cleaner to the gas tank and run the mower to circulate the cleaner. This can break down contaminants and gunk inside the fuel system.

Remove and Clean the Carburetor

Fully removing and cleaning the carburetor can allow you to manually clean out any fuel deposits inside. Follow the steps in your mower’s owner’s manual to properly remove the carburetor. Then clean all jets, ports, and passageways with carburetor cleaner fluid and compressed air.

Replace the Fuel Filter

If you haven’t already, install a new fuel filter. Any debris from bad gas can contaminate the filter. Replacing it removes this contamination source.

Add a Fuel Inline Filter

Adding an inline fuel filter between the tank and carburetor provides extra filtration that can catch remaining contaminants. Allow the mower to run with the inline filter installed to further clear out debris.

Flush the Fuel Tank

To fully clean out the fuel tank, you may need to flush it out. Add some fresh gasoline and carburetor cleaner to the tank. Seal the openings and shake the tank vigorously. Dump out the cleaner and repeat the process until the drained liquid is clear of debris.

Clean the Spark Plug

Fouled spark plugs are a common issue with bad gasoline. Remove the plug and spray it down with carburetor cleaner. Use a small wire brush to gently clean the electrode. Allow it to fully dry before reinstalling.

Preventing Bad Gasoline Issues

To avoid future issues with deteriorated gasoline, follow these gas storage tips:

• Only purchase the amount of gas you know you will use within 30 days
• Store gas in an airtight, sealed container to limit air exposure
• Add fuel stabilizer to gas containers during storage
• Always fill your mower with fresh gas at the start of the mowing season
• Avoid storing gas for prolonged periods if possible

Following proper fuel storage procedures will keep your gasoline fresh and stable when the mower is not in use.

When to Take Your Mower to a Mechanic

If you are still experiencing issues after trying all the steps above, it’s best to have your lawn mower serviced by a professional:

• Engine still will not start
• Engine runs rough or misfires
• Loss of engine power
• Excessive smoke from exhaust

Damaged fuel system components may need replacement by a trained technician at this point. For example, the fuel pump, carburetor, or fuel injectors may need rebuilding or replacing.

Conclusion

Accidentally using old or bad gasoline in your lawn mower can cause performance issues. But with quick action, including draining the fuel system and adding fresh gas and cleaner, you can often resolve the problem yourself. Just be sure to always use fuel stabilizer to keep stored gas from deteriorating. And if symptoms persist after attempted cleaning, have a professional mechanic service the mower to assess for damaged parts.