How to Start Your Mower After Bad Gas: A Comprehensive Guide

Bad gasoline. It’s the bane of every lawn care enthusiast’s existence. You go to start your mower, expecting that familiar roar, and instead you’re met with sputtering, choking, or worse, complete silence. Don’t panic! Bad gas is a common problem, and with a bit of know-how, you can often get your mower running again without a costly trip to the repair shop. This comprehensive guide will walk you through the steps of diagnosing the issue and getting your mower back in action.

Table of Contents

Understanding the Problem: What is “Bad Gas”?

Before we dive into the solutions, let’s understand what we mean by “bad gas.” Gasoline, especially when left sitting for extended periods, degrades. Several factors contribute to this degradation:

Evaporation: Lighter, more volatile components of gasoline evaporate over time, leaving behind heavier, less combustible substances.
Oxidation: Gasoline reacts with oxygen, forming gum and varnish deposits that can clog fuel lines and carburetors.
Ethanol Absorption: Ethanol, often added to gasoline, readily absorbs water. Water in the fuel system can lead to corrosion and starting problems. This is especially problematic in humid environments.

These factors combine to create a fuel that is difficult, if not impossible, for your mower to ignite properly. The symptoms can range from difficulty starting to poor performance and stalling.

Diagnosing the Issue: Is It Really Bad Gas?

While bad gas is a common culprit, it’s essential to confirm that it is indeed the problem before you start tearing things apart. Other potential causes of starting problems include a dead battery, a clogged air filter, a faulty spark plug, or a more serious mechanical issue.

Here’s a simple diagnostic process:

Check the Fuel: Visually inspect the fuel in the tank. Does it look cloudy, discolored, or have a strange odor? Bad gas often has a noticeable difference in appearance compared to fresh gasoline. Smell is a key indicator. Stale gas often has a sour or varnish-like smell.
Consider the Age of the Fuel: How long has the gas been sitting in the tank? If it’s been more than a month or two, especially during the off-season, it’s highly suspect. Fuel stabilizers can help prolong the life of gasoline, but they’re not a miracle cure.
Inspect the Spark Plug: A fouled spark plug can prevent the engine from starting, even with good gas. Remove the spark plug and inspect the electrode. Is it clean, or is it coated with carbon deposits or oil? A dirty spark plug needs to be cleaned or replaced.
Check the Air Filter: A clogged air filter restricts airflow to the engine, which can also cause starting problems. Remove the air filter and inspect it. If it’s dirty, clean or replace it.
Try Starting Fluid: As a last resort diagnostic tool, try spraying a small amount of starting fluid into the air intake. If the engine starts briefly on starting fluid, it’s a strong indication that the fuel system is the problem. Use starting fluid sparingly and with caution, as it can be harmful to the engine if used excessively.

If you’ve ruled out other potential issues and the fuel looks and smells suspect, then it’s likely that bad gas is the culprit.

The Solution: Step-by-Step Guide to Starting Your Mower

Once you’ve determined that bad gas is the problem, here’s how to get your mower running again:

Step 1: Drain the Old Fuel

The first and most important step is to remove the bad gas from the fuel tank.

Safety First: Work in a well-ventilated area, away from any open flames or sources of ignition. Gasoline is highly flammable. Wear safety glasses and gloves to protect yourself.
Locate the Fuel Drain: Most mowers have a fuel drain plug or valve located at the bottom of the fuel tank or carburetor. Consult your owner’s manual for the exact location. If there isn’t a drain plug, you may need to siphon the fuel.
Drain the Fuel: Place a suitable container (approved for gasoline) under the drain. Open the drain plug or valve and allow the fuel to drain completely. If you’re siphoning, use a siphon pump to avoid getting gasoline in your mouth.
Dispose of Fuel Properly: Take the old gasoline to a recycling center or hazardous waste disposal facility. Never pour gasoline down the drain or into the ground.

Step 2: Clean the Fuel System

Simply draining the old fuel may not be enough. Gum and varnish deposits can still be present in the fuel lines and carburetor.

Fuel Line Inspection: Disconnect the fuel line from the carburetor and inspect it for any clogs or restrictions. You can use compressed air to blow out any debris. Replace the fuel line if it is cracked or damaged.
Carburetor Cleaning: The carburetor is a critical component that mixes fuel and air. If it’s clogged, the engine won’t start or run properly.
- Carburetor Cleaner: Purchase a can of carburetor cleaner from an auto parts store. Follow the instructions on the can.
- Spraying: Spray the carburetor cleaner into the carburetor’s intake and any visible orifices. Let it soak for a few minutes to dissolve any deposits.
- Professional Cleaning (Optional): If the carburetor is severely clogged, you may need to disassemble it and clean each component individually. This requires some mechanical skill and knowledge. If you’re not comfortable doing this, take the mower to a qualified repair technician.
- Reassembly: If you disassembled the carburetor, carefully reassemble it, making sure all parts are in their correct positions.

Step 3: Replace the Fuel Filter (If Applicable)

Some mowers have a fuel filter located in the fuel line. If your mower has one, it’s a good idea to replace it at this time. A clogged fuel filter can restrict fuel flow, even with fresh gasoline.

Locate the Filter: The fuel filter is usually located in the fuel line between the fuel tank and the carburetor.
Replace the Filter: Disconnect the fuel line from both ends of the filter. Install a new fuel filter, making sure the arrow on the filter points in the direction of fuel flow (towards the carburetor).

Step 4: Add Fresh Fuel

Now it’s time to add fresh, clean gasoline to the fuel tank.

Use the Correct Octane: Consult your owner’s manual for the recommended octane rating. Using the wrong octane can affect performance and engine life.
Add Fuel Stabilizer: Adding a fuel stabilizer to the gasoline will help prevent it from degrading quickly. Follow the instructions on the stabilizer container. This is especially important if you’re storing the mower for an extended period.
Fill the Tank: Fill the fuel tank to the recommended level, as indicated in your owner’s manual.

Step 5: Prime the Engine

Priming the engine introduces fuel into the carburetor, making it easier to start.

Primer Bulb: Most mowers have a primer bulb located on the carburetor or nearby. Press the primer bulb several times (usually 3-5 times) to prime the engine.
Choke: If your mower has a choke, engage it to restrict airflow and enrich the fuel mixture.

Step 6: Start the Engine

Now, try starting the engine.

Pull Start: If your mower has a pull start, pull the starter rope firmly and smoothly. Avoid yanking the rope, as this can damage the starter mechanism.
Electric Start: If your mower has an electric start, turn the key or press the start button.
Troubleshooting: If the engine doesn’t start after a few attempts, try the following:
- Check the Spark Plug: Make sure the spark plug is properly connected and firing.
- Adjust the Choke: Try adjusting the choke setting. Sometimes, the engine needs a slightly different fuel mixture to start.
- Check for Fuel Leaks: Inspect the fuel lines and carburetor for any fuel leaks.

Step 7: Fine-Tuning

Once the engine starts, let it run for a few minutes to warm up.

Adjust the Throttle: Adjust the throttle to the desired speed.
Listen for Unusual Noises: Listen for any unusual noises that could indicate a problem.
Monitor Performance: Monitor the engine’s performance. Does it run smoothly, or does it sputter or stall?

Preventing Future Problems: Storage and Maintenance Tips

Preventing bad gas from forming in the first place is the best approach. Here are some tips for storing and maintaining your mower:

Use Fuel Stabilizer: Always add fuel stabilizer to the gasoline when storing the mower for an extended period (e.g., over the winter).
Drain the Fuel Tank: Alternatively, you can drain the fuel tank completely before storing the mower. This prevents the gasoline from degrading over time.
Run the Engine Dry: If you choose to drain the fuel tank, run the engine until it stalls to ensure that all the fuel is removed from the carburetor.
Store in a Cool, Dry Place: Store the mower in a cool, dry place to minimize fuel degradation.
Regular Maintenance: Perform regular maintenance on your mower, including changing the oil, cleaning the air filter, and replacing the spark plug.
Use Fresh Gasoline: Always use fresh gasoline in your mower. Avoid using gasoline that has been sitting for more than a month or two.
Ethanol-Free Gasoline: If available in your area, consider using ethanol-free gasoline. Ethanol attracts water, which can lead to corrosion and starting problems.

When to Call a Professional

While many bad gas issues can be resolved with a bit of DIY, there are times when it’s best to call a professional.

Serious Engine Problems: If you suspect a more serious engine problem, such as a damaged piston or valve, it’s best to take the mower to a qualified repair technician.
Complex Carburetor Issues: If you’re not comfortable disassembling and cleaning the carburetor, or if the carburetor is severely damaged, it’s best to let a professional handle it.
Recurring Problems: If you’re constantly having problems with bad gas, even after following the preventive measures outlined above, it’s possible that there’s an underlying issue with your mower’s fuel system. A professional can diagnose and repair the problem.

Dealing with bad gas in your lawnmower can be frustrating, but with a systematic approach, you can often get your mower running again without too much trouble. Remember to prioritize safety, follow the steps carefully, and don’t hesitate to seek professional help if needed. With a little preventative maintenance, you can minimize the chances of encountering this problem in the future and keep your mower running smoothly for years to come.

What are the initial signs that my lawn mower is suffering from bad gas?

The most common signs that your lawn mower is suffering from bad gas are difficulty starting, sputtering during operation, and a general lack of power. You might also notice a strong, unusual odor emanating from the mower, indicating that the fuel has begun to break down or has become contaminated. In severe cases, the engine may stall frequently or refuse to start altogether.

Beyond these immediate performance issues, bad gas can also lead to long-term damage. It can cause corrosion in the fuel lines, carburetor, and other engine components. This corrosion can eventually lead to costly repairs or even necessitate a full engine replacement. Therefore, recognizing the symptoms early is crucial for mitigating potential damage.

How can I safely drain the old, bad gas from my lawn mower’s fuel tank?

First and foremost, safety is paramount. Always work in a well-ventilated area away from any sources of ignition, such as sparks, open flames, or electrical appliances. Disconnect the spark plug wire to prevent accidental starting. Then, carefully locate the fuel shut-off valve (if your mower has one) and close it. Next, position a suitable container, such as an approved gasoline container, below the fuel tank or fuel line.

If your mower has a fuel line that can be easily disconnected, detach it and let the old gas drain into the container. If not, you may need to siphon the gas out using a siphon pump. Once all the old gas has been drained, properly dispose of it according to local regulations. Do not pour it down drains or onto the ground, as this is harmful to the environment.

What is the best way to clean the carburetor after using bad gas?

Cleaning the carburetor is crucial for removing any residue or varnish left behind by bad gas. Begin by carefully disassembling the carburetor, taking note of the placement of each component to ensure proper reassembly. Use carburetor cleaner to thoroughly spray all the parts, including the jets, bowls, and passages. Pay close attention to any areas with visible buildup or corrosion.

For stubborn deposits, consider using a small brush or a piece of wire to gently scrub the affected areas. Allow the carburetor cleaner to soak for a few minutes before rinsing it thoroughly. Once cleaned, reassemble the carburetor according to your notes or a service manual, ensuring all components are properly tightened. This will help restore the proper fuel-air mixture for optimal engine performance.

What type of fuel stabilizer should I use, and how often should I add it?

Choose a fuel stabilizer specifically designed for small engines, as these are formulated to address the unique challenges of lawn mower fuel systems. Look for products that boast protection against ethanol damage and prevent fuel degradation. Reputable brands often offer stabilizers that can keep your fuel fresh for up to 24 months.

Add fuel stabilizer every time you fill up your lawn mower’s gas tank, especially if you don’t use the mower frequently. Follow the manufacturer’s instructions on the stabilizer bottle for the correct dosage. For seasonal storage, add a double dose to ensure maximum protection against fuel breakdown and component corrosion during the off-season.

How can I prevent bad gas from occurring in the future?

The best way to prevent bad gas is to use fresh gasoline. Purchase fuel in smaller quantities to avoid having it sit unused for extended periods. Try to buy gas from stations with high turnover, as this indicates that the fuel is likely fresher. Avoid using gasoline that has been stored for more than 30 days without a fuel stabilizer.

Another key prevention method is proper storage. Store gasoline in a sealed, approved container in a cool, dry place away from direct sunlight. This helps to minimize evaporation and oxidation, which contribute to fuel degradation. Consider using ethanol-free gasoline if it’s available in your area, as ethanol can attract moisture and cause fuel system problems.

If my lawn mower still won’t start after cleaning the carburetor and using fresh gas, what else could be the problem?

If the lawn mower refuses to start even after cleaning the carburetor and using fresh gas, there may be other underlying issues preventing ignition. Check the spark plug to ensure it’s clean and properly gapped. A faulty spark plug will not ignite the fuel-air mixture. Also, inspect the air filter to make sure it’s not clogged, which can restrict airflow and prevent the engine from starting.

Another potential problem could be a compression issue. A leak in the cylinder can prevent the engine from building enough pressure to ignite the fuel. If you suspect a compression problem, it’s best to consult a qualified mechanic. Finally, check the fuel lines for any blockages or leaks, which can prevent fuel from reaching the carburetor. Addressing these potential issues can often restore your lawn mower to proper working order.

When should I consult a professional mechanic instead of attempting to fix the bad gas issue myself?

If you lack experience in small engine repair or feel uncomfortable working on your lawn mower’s engine, it’s always best to consult a professional mechanic. Additionally, if you’ve attempted the basic troubleshooting steps, such as draining the gas, cleaning the carburetor, and replacing the spark plug, and the mower still won’t start, it’s likely there’s a more complex issue requiring specialized tools and expertise.

Furthermore, if you notice any signs of severe engine damage, such as a knocking sound or excessive smoke, it’s crucial to seek professional help immediately. Continuing to run the engine in such a condition could cause further damage and lead to costly repairs. A qualified mechanic can accurately diagnose the problem and provide the necessary repairs to get your lawn mower back in working condition.