There are two main scenarios where people may suspect that the gas in their ATV is bad. One is when the bike suddenly begins displaying strange, performance-related issues where the engine won’t run properly. The other is when taking the ATV out from storage after a long and harsh winter season. The ATV may not start, or you just want to make sure the gas left in the bike is still good to use. 

Sometimes you can tell whether the gas is good or bad from the ATV’s symptoms when running the bike. You can also use your senses to inspect the gas to see if it shows signs of staling. 

When an ATV suddenly begins displaying symptoms like difficulty starting, rough idling, or sluggishness, it may have gotten bad gas into the tank. Gas that is bad from old age smells like turpentine and becomes darker than fresh gas.

What Do We Mean by Bad Gas?

Before we take a closer look at the signs and symptoms of bad gas, it’s good to know what we mean when talking about “bad” gas or gas going bad. 

While modern gas may begin to break down after only a month or two, it is still considered “good” for a long time. The gas is not regarded as bad before it causes noticeable signs of reduced engine performance.

According to NACS – a leading global fuel trading association serving as a trusted advisor to over 1,500 retailers and 1,600 supplier members from more than 50 countries, the term “bad gas” applies to fuel that won’t properly combust.

Like any other gas-powered vehicle, an ATV gets its power from a complex combustion process that requires an electric spark, compressed air, and high-quality fuel vapors to take effect. 

If the spark is weak, compression is bad, or the fuel vapors for some reason do not possess the required quality, the ignition process gets interrupted, leading to poor or suboptimal engine performance.

How Does Gas Go Bad in an ATV?

There are several ways gas can go bad in the sense where it won’t combust properly. In ATVs, the most common is when the gas goes bad from old age or gets contamination by a foreign substance.

Gas Going Bad From Old Age

Gas is considered fresh produce, which can go bad over time. It’s a highly refined product made with a complex mix of many different hydrocarbons such as butane, pentane, benzene, ethylbenzene, and more.

One crucial characteristic that gasoline possesses is high volatility, which indicates how easily the fuel vaporizes. As discussed above, the combustion process requires vaporized fuel for it to burn fuel efficiently.

Over time, the lighter hydrocarbons that aid in making the gasoline highly volatile tend to evaporate, causing an imbalance in the mixture. The fuel becomes less volatile, and its ability to combust degrades until it no longer will ignite and burn properly.

While you may be able to start and run your ATV on fuel with reduced volatility, it will likely not perform as well.

While some of the lighter hydrocarbons evaporate into the air, some of the heavier hydrocarbons react with oxygen, creating new components that lead to gum and varnish deposits in the fuel lines, filters, and carburetor. 

This may lead to fuel delivery issues which come on top of the poor performance caused by reduced fuel volatility. 

US-Gas Containing Ethanol Going Bad

Most of the gas sold in the USA contains Ethanol which makes up anything from 10% (E10) up to as much as 85% (E85) of the blend.

Where hydrocarbons bond with oxygen molecules, Ethanol bonds with water vapor in the air, leaving the gas contaminated with water.

Not only does water disrupt the combustion process, but it may also cause internal corrosion inside metal fuel tanks or the engine. 

Gas Getting Contaminated Water

It’s not only from fuel that contains Ethanol, where water can get into your gas tank and engine. 

A leaky gas cap can allow water into the tank from heavy rain, washing with a pressure washer, or submerging the ATV in mud or water. 

Condensation inside the fuel tank from rapid temperature swings is another potential cause of water contaminating the fuel.

There is also a slight chance that the fuel you get at the gas station already has some water due to delivery or storage issues. 

As you can imagine, it doesn’t matter how water gets mixed with the fuel. When this happens, the fuel is considered compromised and needs to be replaced with fresh gas. 

Filling up With a Lower Octane Level Than Required

All ATVs need fuel with a specified octane level to run properly. There’s always a chance that the tank was filled with gas of a lower octane rating intentionally or accidentally. 

One scam performed by some dishonest gasoline retailers is filling regular gas in the high octane underground tank. In some cases, the retailer was honest, but the distributor ripped them off by delivering lower octane fuel than specified. 

Luckily, this is not considered standard practice. You are more likely to choose the wrong handle at the pump by accident. 

Gas Getting Contaminated With Dirt or Debris

The final of the most common ways gas in ATVs goes bad is when it gets contaminated with dirt or small sediments from various sources.

While screens and fuel filters capture the majority of larger particles, there is a risk that the smallest particles may get through and clog fuel injectors or carburetor jets over time. 

Dirt or sediment contamination can occur anywhere from the refinery, delivery truck, gas station, a storage container, or leaky gas cap.

What Are the Symptoms of Bad Gas?

Often, you may begin to suspect bad fuel when noticing strange symptoms and behavior when starting or riding. Symptoms of bad gas in an ATV include:

  • Difficulty starting up
  • Rough idling
  • Pinging sounds
  • Stalling
  • Sputtering
  • Sluggishness
  • Check-engine light illumination. ATVs with electronic fuel injection (EFI) can sense when combustion is off and will alert you by illuminating the check-engine light.
  • Reduced fuel economy. The ATV attempt to compensate for bad combustion by adding more fuel
  • Higher emissions. When unburnt fuel passes through the engine and into the exhaust system. 

How to Test if Your Gas Is Bad – Look For These Signs

The best way to test if gas has gone bad is by using your senses. 

Siphon a small amount of the suspected fuel into a clean, see-through container to inspect it. Fill fresh gas into a separate container for comparison. 

  • Compare Smell. The smell is often the easiest way to identify bad gas. If the gas smells harsh, with a smell comparable with turpentine, the gas has likely gone bad and should not be used. Others describe bad gas as smelling sour or like pungent varnish. Use the fresh gas as a reference. You will notice it smells more like solvents. With experience, you will be able to smell the difference without smelling fresh gas each time.
  • Compare Color. In time, gas gradually changes to a darker color. It may be hard to tell the difference without having fresh gas available for comparison. 
  • Compare Clarity. Good gas should be clear. If it’s foggy, it may be contaminated with water or other sediments. 

How Long Does Gas Stay Good in an ATV?

There is no definite rule for how long gas can be stored or left in the tank before it is no longer good. 

Environmental factors such as humidity, temperature, and oxygen exposure all impact how long gas stays fresh and usable. 

Also, there is no way of knowing how old the gas you bought at the pump is; it may be fresh or a month or two already. 

As a rule of thumb, you’re likely better off not using gas that is older than one year. 

However, gas stored in less ideal conditions can degrade quickly and may start showing signs of going bad after only a few months.

On the other hand, gas stored in the rights conditions may be good even after several years of storage. 

How to Fix Bad Gas in an ATV

Old or bad gas needs to be removed from the tank and replaced with fresh fuel. If the tank on your ATV has a drain plug or accessible petcock valve, simply use that to drain the tank completely. 

Most modern ATVs do not, however, have an easily accessible drain plug. 

In that case, use this method:

  1. Begin by siphoning out as much gas as possible from the tank and into a container. Make sure to dispose of the old gas at a recycling station.
  2. Disconnect the fuel line by the carb or where it goes into your EFI, and allow the remaining fuel to drain out. 
  3. Flush the tank with a small amount of fuel and allow that to drain as well. 
  4. Reconnect the fuel fittings and add fresh fuel to the tank. 

Tip 1: On EFI bikes, you may need to run the fuel pump for a couple of seconds for the fuel to drain. Activate the pump by turning the ignition key until the pump starts, but do not turn the key all the way to “run”. 

Tip 2: Another way of draining the tank is by sticking a drain hose and an air hose down into the tank to use compressed air to force the fuel out of the tank. Use rags to seal off the tank opening and gently apply air until fuel start draining out the hose and into a container. Then use a grab-it-tool and some shop rags to mop out the remaining fuel in the tank.

Tip 3: If there is only a tiny amount of bad gas in the tank, adding fresh gas and some Seafoam to clean the carb and fuel lines may be all that you need to do. In some severe cases, you may need to disassemble and clean the carb. Pay close attention to the needle seats and clean the pilot jets. You may need to replace the needles and jets.

Tip 4: The fuel in the carb typically goes bad before the gas in the tank. Use starting fluid to force the ATV to burn through the relatively small amount of bad fuel in the carb and allow fresh fuel to enter.

How to Prevent Gas From Going Bad

Add Fuel Stabilizer Before Long Term Storage

Before putting your ATV away for the winter, make sure to add a high-quality fuel stabilizer to the tank, such as Stabil or Startron.

Note that fuel stabilizers do not revitalize gas that has already gone bad. It will only aid in keeping good gas fresh longer by slowing down hydrocarbon evaporation.

After adding the stabilizer to the tank, go for a short ride to allow treated fuel to enter the carburetor. 

Store the Gas Properly

As gasoline is highly volatile and thereby highly flammable, it is never a good idea to store large amounts of gasoline at home. Make sure to store any gas you keep at home in a cool, low-oxygen environment, such as an airtight container designed for fuel storage kept in a cool garage. 

Use Ethanol Free Gas

Whenever possible, use ethanol-free gas on any vehicle that regularly sits without being used, such as an ATV.

Alternatively, drain ethanol-based gas before storage, and use it in your car. 

Don’t Use “Winter Gas” in the Summer

The gas sold in the summer is not the same as the one sold in winter. Summer gas contains heavier hydrocarbons to prevent premature evaporation, while winter gas contains lighter hydrocarbons to aid combustion through the cold winter months. 

The lighter hydrocarbons in winter gas will evaporate quickly in the summer, causing the gas to go bad prematurely.

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I'm an ATV and offroad-enthusiast, an engineer, a farmer, and an avid home-mechanic. I'm also the owner and editor of BoostATV.com. If you have any questions or suggestions regarding this article, please feel free to contact me.