Lawn mowers, the unsung heroes of suburban landscapes, are often taken for granted until they sputter, cough, and refuse to start. One of the most common culprits behind these frustrating malfunctions? Bad gas. Gasoline, unlike fine wine, doesn’t improve with age. In fact, it deteriorates, leading to a host of engine problems. But don’t despair! This comprehensive guide will walk you through diagnosing and fixing bad gas issues in your lawn mower, ensuring a smooth and efficient mowing season.
Understanding the Enemy: What Makes Gas “Bad”?
Gasoline isn’t just a simple liquid; it’s a complex blend of hydrocarbons designed to ignite readily and power your engine. However, several factors can compromise its integrity over time.
The Evaporation Problem
Gasoline is volatile, meaning it evaporates easily. Lighter hydrocarbons, responsible for easy starting, are the first to disappear. This leaves behind heavier, less combustible components, making the fuel harder to ignite, especially in colder conditions. This process is accelerated by heat and improper storage. Leaving your mower with gas sitting in the tank over the winter is a recipe for trouble.
Oxidation: The Rust of Fuel
Just like metal, gasoline oxidizes when exposed to air. This process creates gum and varnish, sticky residues that can clog fuel lines, carburetors, and other vital engine parts. These deposits restrict fuel flow, leading to poor performance or complete engine failure. The longer the gas sits, the more significant the oxidation becomes.
Ethanol’s Double-Edged Sword
Many modern gasolines contain ethanol, an alcohol added to increase octane and reduce emissions. While ethanol has its benefits, it also has drawbacks. It’s hygroscopic, meaning it readily absorbs water from the atmosphere. This absorbed water can lead to phase separation, where the ethanol and water separate from the gasoline, forming a corrosive layer at the bottom of the tank. This water-ethanol mixture is extremely detrimental to small engines, causing rust, corrosion, and fuel system damage. Ethanol-free gasoline is often recommended for small engines.
Identifying the Symptoms: Is It Really Bad Gas?
Before you tear apart your lawn mower, it’s crucial to confirm that bad gas is indeed the problem. Several telltale signs can point you in the right direction.
Difficulty Starting
This is the most common symptom. The engine may crank and crank but fail to ignite, or it might start briefly and then stall. The evaporated light hydrocarbons or the presence of water makes ignition difficult.
Rough Running and Stalling
If the engine does start, it might run unevenly, sputtering, coughing, or lacking power. This is due to the gum and varnish deposits clogging the fuel system and preventing a smooth, consistent fuel flow. The engine might stall frequently, especially under load.
Unusual Smells
Old or contaminated gasoline can have a sour, pungent, or varnish-like odor, quite different from the fresh, clean smell of new gas. This is a strong indicator that the fuel has deteriorated.
Visible Debris in the Fuel Tank
Inspect the fuel tank for visible signs of contamination, such as rust particles, sediment, or a cloudy appearance. Phase separation, where the water and ethanol have separated from the gasoline, will appear as a distinct layer at the bottom of the tank.
The Fix: Steps to Remedy Bad Gas Issues
Once you’ve confirmed that bad gas is the likely culprit, it’s time to take action. The following steps outline a comprehensive approach to resolving the problem.
Step 1: Drain the Old Fuel
The first and most important step is to remove the contaminated fuel from the tank.
Disconnect the spark plug wire: This is crucial for safety to prevent accidental starting while working on the fuel system.
Locate the fuel shut-off valve: Most lawn mowers have a fuel shut-off valve located near the fuel tank. Turn it to the “off” position.
Drain the fuel tank: Use a siphon pump or carefully tilt the mower (with the air filter facing upwards to avoid flooding the engine) to drain the fuel into a suitable container, such as an approved gasoline can. Dispose of the old fuel properly at a hazardous waste collection facility. Never pour old gasoline down the drain or into the ground.
Step 2: Clean the Fuel Tank
Even after draining, some residue may remain in the fuel tank.
Rinse the tank: Pour a small amount of fresh gasoline into the tank and swish it around to loosen any remaining debris. Then, drain the gasoline completely.
Inspect for rust: Carefully inspect the inside of the tank for rust or corrosion. If rust is present, you may need to use a fuel tank cleaner specifically designed for removing rust.
Dry the tank: Allow the tank to air dry completely before refilling it with fresh fuel.
Step 3: Clean or Replace the Fuel Filter
The fuel filter prevents contaminants from entering the carburetor. A clogged fuel filter will restrict fuel flow and cause the same symptoms as bad gas.
Locate the fuel filter: The fuel filter is usually located in the fuel line between the fuel tank and the carburetor.
Inspect the fuel filter: If the filter is transparent, you can visually inspect it for dirt and debris. If it’s opaque, you’ll need to remove it to inspect it.
Clean or replace: If the filter is only slightly dirty, you can try cleaning it with carburetor cleaner. However, if it’s heavily clogged or damaged, it’s best to replace it with a new one. Always use the correct type of fuel filter for your lawn mower model.
Step 4: Clean the Carburetor
The carburetor mixes air and fuel in the correct proportions for combustion. Gum and varnish deposits from bad gas are a common cause of carburetor problems.
Locate the carburetor: The carburetor is usually located between the air filter and the engine.
Remove the carburetor (optional): While some carburetors can be cleaned without removal, it’s often easier and more thorough to remove it. If you’re not comfortable removing the carburetor, consult your owner’s manual or a qualified mechanic.
Disassemble the carburetor (if removed): Carefully disassemble the carburetor, taking note of the location of each part. It’s helpful to take pictures as you go to ensure proper reassembly.
Clean the carburetor parts: Use carburetor cleaner to thoroughly clean all carburetor parts, paying particular attention to the jets, passages, and float bowl. Use a small wire or carburetor cleaning tool to clear any blockages.
Reassemble the carburetor: Carefully reassemble the carburetor, ensuring that all parts are properly seated and tightened.
Reinstall the carburetor (if removed): Reinstall the carburetor on the engine, connecting all fuel lines and linkages.
Step 5: Replace the Spark Plug (Optional but Recommended)
A fouled spark plug can also contribute to starting and running problems. While cleaning the spark plug is an option, replacing it is often the best solution, especially if it’s old or damaged.
Locate the spark plug: The spark plug is located on the engine cylinder head.
Remove the spark plug: Use a spark plug wrench to remove the spark plug.
Inspect the spark plug: Check the spark plug for signs of fouling, such as carbon buildup, oil deposits, or a cracked insulator.
Replace the spark plug: Install a new spark plug of the correct type and gap for your lawn mower model. Refer to your owner’s manual for the correct spark plug specifications.
Step 6: Add Fresh Fuel and Fuel Stabilizer
Fill the fuel tank with fresh, high-quality gasoline. Consider using ethanol-free gasoline, especially if you live in an area with high humidity or plan to store the mower for an extended period. Add a fuel stabilizer to the gasoline. Fuel stabilizers prevent the gasoline from deteriorating and help to keep the fuel system clean. Follow the manufacturer’s instructions for the correct amount of fuel stabilizer to add.
Step 7: Start the Engine
Reconnect the spark plug wire. Turn the fuel shut-off valve to the “on” position. Start the engine. It may take a few attempts for the engine to start, especially if the carburetor was disassembled. Once the engine starts, let it run for a few minutes to allow the fuel system to clear.
Preventing Future Problems: Tips for Proper Fuel Storage
Preventing bad gas is far easier than fixing it. By following these simple tips, you can keep your lawn mower running smoothly for years to come.
Use Fresh Fuel
Avoid using gasoline that has been stored for more than 30 days. Buy only the amount of gasoline you need for the season.
Store Fuel Properly
Store gasoline in an approved gasoline container in a cool, dry, and well-ventilated area. Keep the container tightly sealed to prevent evaporation and contamination.
Use Fuel Stabilizer
Add fuel stabilizer to gasoline, especially if you plan to store the mower for an extended period, such as over the winter.
Run the Mower Dry (or Nearly Dry) Before Storage
Before storing the mower for the winter, run it until the fuel tank is nearly empty. This will minimize the amount of gasoline that can deteriorate. Alternatively, drain the fuel tank completely.
Consider Ethanol-Free Gasoline
If possible, use ethanol-free gasoline in your lawn mower. This will eliminate the risk of phase separation and corrosion. Ethanol-free gasoline is particularly beneficial for small engines that are used infrequently.
By following these steps, you can effectively diagnose and fix bad gas issues in your lawn mower. Remember that regular maintenance, including proper fuel storage, is the key to keeping your lawn mower running smoothly and reliably. With a little care and attention, you can enjoy a hassle-free mowing season for years to come.
Why does bad gas cause problems in my lawn mower?
Gasoline degrades over time, especially when mixed with ethanol. As it degrades, it forms gums and varnishes that can clog fuel lines, carburetors, and fuel injectors in your lawn mower. This leads to poor engine performance, difficulty starting, and eventually, complete engine failure if left unaddressed.
Furthermore, the ethanol in old gasoline attracts moisture, leading to water separation within the fuel tank. This water can corrode internal engine parts and prevent the mower from starting, as water is not combustible and disrupts the fuel-air mixture needed for ignition. The resulting sludge can also cause significant damage to the engine.
How long can gasoline sit in my lawn mower before it goes bad?
Generally, untreated gasoline can start to degrade within 30 days, especially when exposed to air and temperature fluctuations. Gasoline blended with ethanol tends to degrade even faster, potentially becoming unusable in as little as two to three weeks. This is because ethanol readily absorbs moisture from the air, accelerating the degradation process.
Therefore, if you anticipate your lawn mower sitting idle for more than a month, it’s crucial to either stabilize the gasoline with a fuel stabilizer or completely drain the fuel tank and carburetor. This prevents the formation of harmful deposits and protects the engine from corrosion and other damage caused by degraded fuel.
What are the signs that my lawn mower has bad gas?
One of the most noticeable signs of bad gas in your lawn mower is difficulty starting the engine. You might find yourself pulling the starter cord repeatedly without success, or the engine may start briefly and then stall. This is often due to clogged fuel lines or a malfunctioning carburetor caused by the degraded fuel.
Other common symptoms include rough idling, sputtering, a lack of power when cutting grass, and unusual exhaust smells. The engine might also hesitate or surge erratically. If you observe any of these signs, it’s highly likely that the gasoline in your lawn mower has deteriorated and needs to be addressed.
Can I simply add fresh gas to bad gas to fix the problem?
Adding fresh gasoline to old, degraded gasoline is generally not recommended as a solution. While it might dilute the bad gas slightly, it won’t reverse the damage that has already occurred, such as the formation of gums and varnishes in the fuel system. These deposits can still clog fuel lines and carburetor jets, leading to continued performance issues.
Furthermore, adding fresh gas won’t remove any water that has separated from the gasoline due to ethanol absorption. The remaining old gas will continue to degrade, further contaminating the fresh fuel. It’s always best to completely remove the bad gas and clean the fuel system before adding fresh, stabilized gasoline.
How do I properly drain the bad gas from my lawn mower?
First, ensure the lawn mower is turned off and the engine is cool. Disconnect the spark plug wire for safety. Then, locate the fuel shut-off valve (if equipped) and turn it off. Place a suitable container beneath the fuel line connection at the carburetor. Disconnect the fuel line and allow the fuel to drain completely into the container.
If your lawn mower doesn’t have a fuel shut-off valve, you can use a fuel siphon to remove the gas from the fuel tank. Carefully insert the siphon hose into the tank and pump the fuel into the container. Be sure to dispose of the old gasoline properly at a designated recycling center or hazardous waste facility. Never pour it down a drain or onto the ground.
What is a fuel stabilizer and how does it work?
A fuel stabilizer is a chemical additive designed to prevent gasoline from degrading over time. It works by inhibiting the oxidation process that leads to the formation of gums, varnishes, and other harmful deposits. Fuel stabilizers also help to prevent moisture absorption, which is particularly important for gasoline blended with ethanol.
By adding a fuel stabilizer to your gasoline, you can significantly extend its shelf life, often for up to 12-24 months. This helps to ensure that your lawn mower starts easily and runs smoothly, even after periods of inactivity. Always follow the manufacturer’s instructions for the correct dosage when adding fuel stabilizer.
Besides draining the gas, what else should I do to winterize my lawn mower?
In addition to draining the fuel tank and carburetor, consider changing the engine oil before storing your lawn mower for the winter. Old oil can contain acids and contaminants that can corrode internal engine parts. Replacing it with fresh oil provides a protective layer against corrosion.
Also, clean the air filter to ensure proper airflow for the next mowing season. Remove any debris from the mower deck and sharpen or replace the blade. Finally, store the lawn mower in a dry, covered location to protect it from the elements and prevent rust. Properly winterizing your lawn mower will help ensure it starts easily and operates efficiently when you’re ready to use it again.