What Is the Best Thing to Do with Stale Fuel in My Lawnmower?

 

Have you ever pulled out your lawnmower after a long break, only to find that it won’t start? Well, one of the most common culprits behind this frustrating issue is stale fuel. Old petrol in a lawnmower can cause engine trouble, affecting performance and potentially leading to expensive repairs. But don’t worry – if you’re dealing with bad fuel in your lawnmower, you’re in exactly the right place to sort it out.

In this guide, we’ll begin by examining why stale fuel is a problem, including the warning signs that your lawnmower’s fuel might be stale. We’ll then talk you through the process of removing old gas from your lawnmower, before rounding things off by explaining how to prevent these fuel-related issues arising in the future.

Why Is Stale Fuel a Problem?

Over time, petrol in your mower can degrade, often in as little as 2 – 4 weeks. This is because modern petrol contains ethanol, which absorbs moisture from the air, leading to separation and deterioration. When this happens, your mower may struggle to start – or not start at all.

Signs that you might have stale gas in your lawnmower include:

• The mower won’t start despite having fuel.
• The engine sputters or runs poorly.
• A strong, sour smell from the fuel tank.
• Visible sediment or discoloration in the fuel.

If your mower has been sitting unused for a while, it’s likely you’ll need to get old fuel out of your lawnmower before it can run properly again. Let’s go through the steps to fix this issue right now.

How to Remove Stale Fuel from Your Lawnmower

Step 1: Drain the Carburettor

The first thing to check is the carburettor. If your mower has been sitting idle for just a few weeks, draining old gas from the carburettor might be enough to solve the problem.

How to do it:

1. Locate the carburettor, typically near the air filter housing.
2. Find the drain bolt under the float bowl (a small egg-cup-shaped component).
3. Place a suitable container underneath to catch the drained fuel.
4. Loosen the bolt (usually 10mm) anticlockwise to let the fuel drain.
5. Once the fuel stops flowing, refit the bolt and clean up any spills.

At this stage, try starting your mower. If it still doesn’t start, proceed to draining the fuel tank.

Step 2: Drain Old Petrol from the Fuel Tank

If the stale fuel has been in the tank for several months (such as over winter), you’ll need to remove all of it. There are two main ways to do this.

Method 1: Draining via the Fuel Line

1. Locate the fuel tank and the rubber fuel pipe underneath it.
2. Use pliers to squeeze the silver clip and slide it back down the pipe.
3. Carefully pull the fuel pipe away from the tank outlet.
4. Position a suitable jug under the outlet and allow the fuel to drain completely.

Method 2: Siphoning from the Filler Cap

1. If you have a hand-pump siphon, insert one end into the tank and the other into a container.
2. Manually pump the fuel into your container.
3. If you don’t have a siphon, tip the mower while someone else holds a container under the filler cap.

Regardless of the method, ensure you dispose of stale fuel responsibly. Petrol should never be poured down drains or onto the ground – check with your local recycling centre for proper disposal.

Step 3: Re-Drain the Carburettor

After draining the tank, repeat Step 1 to ensure all stale fuel is out of the system.

Step 4: Inspect and Clean the Carburettor (If Needed)

If your mower still refuses to start, old fuel in the lawnmower may have caused blockages in the carburettor. You may need to remove and clean it.

How to clean the carburettor:

1. Remove the air filter box and disconnect any pipes leading to the carburettor.
2. Unscrew the mounting bolts and carefully slide the carburettor off.
3. Remove the float bowl and check for rust or debris.
4. Use carburettor cleaner and compressed air to clean all passages.
5. Reassemble everything in reverse order and reinstall.

If the carburettor is too damaged, consider replacing it. This is often more cost-effective than repeated cleaning attempts.

How to Prevent Stale Fuel Problems

Now that your lawnmower is running again, let’s discuss how to prevent old gas in your mower from causing issues in the future.

1. Use Fresh Petrol

Petrol starts degrading after 30 days. If you don’t use your mower frequently, buy smaller amounts of petrol to avoid it going stale.

2. Consider Ethanol-Free Fuel

We recommend using Aspen Pre-Mixed Fuel, which is a premium ethanol-free alkylate petrol with a very long shelf life. Though more expensive, it prevents carburettor blockages and engine issues.

3. Drain Fuel Before Storage

If you’re putting your mower away for winter, drain old petrol from the tank and carburettor to prevent degradation.

4. Use a Fuel Stabiliser

A fuel stabiliser can extend the life of petrol for several months. Simply add it to your fuel before filling the mower’s tank.

5. Run the Engine Dry

If you can’t drain the fuel, run the mower until it burns through all petrol. This prevents residue build-up in the carburettor.

Visit Ron Smith for a Longer-Lasting Lawnmower!

Stale fuel in a lawnmower can lead to poor performance and costly repairs but, thankfully, it’s a problem that’s relatively easy to fix. And, as you can see from above, it’s a problem that’s even easier to avoid. So, to prevent your fuel going stale and enjoy a longer-lasting, healthier lawnmower, be sure to stock up on our Honda Fuel Stabiliser and Aspen accessories for petrol garden machinery* today.

(*Please note that you can only purchase Aspen Fuel in person, from either our Hereford or Worcester showroom. We do not post this product.)