What’ll Happen if You Put the Wrong Gas in Your Dirt Bike

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Male fills up his dirt bike at the gas station with wrong kind of gas.

If you’ve ever misread the type of fuel at the fuel pump or left your kid in charge of fueling up their own dirt bike, you may have inadvertently ended up with a tank full of the wrong gas. This happens from time to time, but what are the real consequences of doing this? Have you doomed your bike to the junk heap or is there a way to come back from a fueling mistake like this?

Dirt bikes that are filled with the incorrect type of gas may knock, smoke excessively, or suffer internal damage depending on the type of engine and the gas that was mistakenly used.

If you accidentally filled up your dirt bike with the wrong type of gas, it’s not the end of the world (and you certainly aren’t alone). So let’s talk about what will happen in various situations and what you should do about it.

Putting the Wrong Grade of Gas in a Dirtbike

Let’s say you’ve filled up the tank on your dirtbike and just realized you just put in the wrong octane grade. What will happen if you try to ride it now? Well, it all depends on what grade of fuel your bike was meant to run on, and what grade of fuel you actually added instead.

Example Situations

  • A 4-Stroke Dirt Bike Requiring Premium Gas Filled with Regular or Mid-Grade Gas – If your dirt bike is a four-stroke engine that is built to handle premium fuel (91 to 94 octane) and you accidentally filled it with regular fuel (87 octane) or higher, there shouldn’t be any significant consequences as long as you aren’t hearing any knocking or pinging from the engine while you ride, especially while under load. You may notice a slight dip in power/performance but your bike will still be able to run with this type of fuel.
  • A 2-Stroke Dirt Bike Filled with Gas That’s Less Than 90 Octane – If you try to use an octane that’s lower than 90 in a two-stroke engine, you may begin to experience engine knocking. This occurs when the fuel in the engine combusts earlier in the bike’s cylinder than it’s supposed to and it creates a distinct knocking sound. Knocking will cause damage to engine internals with time, so it’s important not to ride your bike if it’s knocking. This knocking sound is most noticeable while the engine is under load (such as accelerating up a steep grade).
  • A Dirt Bike Requiring Premium Fuel Filled with Mid-Grade or Regular Gas – If you use a low octane fuel in a dirt bike that requires premium fuel, knocking could become a severe issue. These early detonations can damage your engine, especially if allowed to occur for extended periods.
  • A Dirt Bike Made for a Lower Octane Fuel Filled with a Higher Octane Fuel – On the other hand, using high octane fuel such as premium fuel in a bike that is meant to run on a lower octane rating isn’t dangerous for your dirt bike’s internals. Your bike will run just fine and may even run slightly better. The worst case is you may have wasted a little money on a fuel that was more expensive than your dirt bike required. So if your bike is built to handle 87 octane, you could pay extra for premium fuel if you choose, but it won’t make much of a difference in performance. 

Don’t be fooled into thinking that high-octane fuel is always the best! Using the recommended fuel type for your bike will help it perform at the proper level without wasting extra money.

For additional information about this topic, check out the video below.

Putting Ethanol Fuel in Your Dirt Bike

All gasoline contains some level of ethanol. However, there are some ethanol-based fuels you may see at your local pump station that have higher levels of ethanol and are therefore usually much cheaper than the other gas options. Fuels with a high ethanol content should not be used in 2-stroke dirt bikes but are generally safe for 4-strokes.

  • Ethanol Fuel in 2-Stroke Dirt Bikes – This is unsafe. The higher concentrations of ethanol will break down the oil that you mix in with the gasoline for your 2-stroke. This means your 2-stroke dirt bike won’t get the lubrication it normally gets and it can easily lead to a damaged or destroyed engine.
  • Ethanol Fuel in 4-Stroke Dirt Bikes – This is generally safe. In 4-stroke dirt bikes, the fuel is not mixed with oil before it goes into the gas tank. Therefor the ethanol doesn’t have a chance to breakdown the oil. Your dirt bike has a seperate resevoir for oil and can stay well lubricated even with the use of heavily ethanol-based fuels.

However, it’s good practice to just avoid ethanol-based fuels in general since they can lead to an increase in corrosion, even in 4-stroke dirt bikes.

If you must use ethanol once in a while, use a low concentration (10% or lower) and don’t make a habit of it.

Putting Diesel in Your Dirt Bike

It’s definitely a bad idea to put diesel in your dirtbike. Diesel is very different from gas and it’s made for an entirely different kind of engine. There are a few models of dirt bikes and motorcycles that may run on diesel, but this isn’t the norm.

If you put diesel in a gas dirt bike, it may not start and even if it does, it will likely smoke heavily and quickly lose power. It may even stall or shoot flames from the exhaust while you’re riding which can be very dangerous and even start a brush fire! In fact, dirt bikes start fires quite frequently for many reasons. Learn about how dirt bikes start fires here.

If you accidentally put diesel in your gasoline dirt bike, turn off the engine and drain the fuel as soon as possible. Do not try to ride the dirt bike or burn off the fuel as it could be dangerous.

Below is a video of a rider who accidentally filled up with Diesel. As you can see, it doesn’t take long for his bike to break down and stall.

Video of a rider who accidentally put diesel in his gas dirt bike.

Putting Unmixed Gas in Your Two-Stroke Dirtbike

Two-stroke dirt bikes are more sensitive and specific to fuel changes than four-stroke models. While four-strokes run fine on gas that comes straight from the pump, two-stroke engines require a pre-made mixture of gasoline and oil. This added oil keeps the engine lubricated and running smoothly.

The owners of two-stroke dirt bikes typically buy oil and fuel separately and mix them together in the appropriate ratios to lubricate the engine while it’s running, usually somewhere between 32:1 and 40:1 (fuel to oil ratio). If a 2-stroke is run on gasoline alone, it won’t be able to lubricate the engine components, which can result in overheating and engine seizing.

Running unmixed fuel in a 2-stroke dirt bike will quickly damage the piston, cylinder, and other components resulting in a loss of compression and eventually complete engine failure.

If you catch the problem early enough, turn off the bike and give the engine time to cool down. Next, you can buy or create a proper fuel mix. You only need a few ounces of oil per gallon to make your two-stroke engine run smoothly.

It’s generally not a good idea to pour oil directly into your fuel tank without mixing it first since it can result in ineffective and inaccurate mixing of the oil and gas. However, if you accidentally filled your two-stroke engine with unmixed gasoline, you could try it if you’re feeling brave (just mix it as well as you can) but it’s always best to drain the tank and refill with correctly mixed gas.

Putting Incorrectly Mixed Fuel in Your Dirt Bike (Fuel to Oil Ratio)

Four-stroke engines have an oil system that enables them to direct oil to their piston and other critical areas for lubrication. This means that they don’t need a specific premix of oil and fuel in order to function properly. 2-Strokes on the other hand, rely on the oil being pre-mixed with gasoline before it goes into the tank.

Here are some various scenarios involving putting incorrectly mixed gasoline into dirt bikes and what the results will be:

  • Mixed 2-Stroke Fuel in a 4-Stroke – Running one tank of premixed 2-stroke fuel in a 4-stroke dirt bike won’t usually cause long-term damage to the bike. However, the bike may smoke additionally while riding and experience poor performance. If this is done often, it may lead to greasy buildup inside the engine and oil leaks.
  • Mixed Fuel with Too High of a Gas to Oil Ratio in a 2-Stroke – Running a 2-stroke dirt bike on fuel with a gas to oil mix ratio that’s too high (meaning there’s too much gas and not enough oil in the mix) can cause damage to internal components of the bike. The severity of this depends on how lacking the fuel is in the amount of oil that the bike was designed for.
  • Mixed Fuel with Too Low of a Gas to Oil Ratio in a 2-Stroke – Running a 2-stroke dirt bike on fuel with a gas to oil mix ratio that’s too low (meaning there’s too much oil and not enough gas) will likely cause additional smoke while riding but wont lead to any damaging long-term affects on the motor.

Remember, if you don’t have enough oil in your bike as compared to what the bike was designed for, the engine won’t be able to self-lubricate properly. This leads to overheating and internal damage. Your engine could seize in as little as just a few minutes. Then you’ll be rebuilding your dirt bike engine.

On the other hand, if you have too much oil, you’ll have fewer issues. Excess oil usually just burns off, so it’s better to use too much as compared to not enough.

Mixing Unleaded and Premium Gas in Your Dirt Bike

If you would prefer to create a custom fuel blend for your dirt bike, and mid-grade gas isn’t available, you might want to mix unleaded and premium gas together. Unleaded fuel (often called “regular gas”) has a lower octane rating. Premium fuel is more expensive and the benefits might not always be worth the cost.

It’s safe to mix unleaded and premium fuel in your dirt bike unless your bike is specifically designed for only high-octane fuel.

Mixing unleaded and premium fuel results in a mid-grade result. It’s a bit cheaper than buying pure premium fuel and it will slightly reduce your chances of knocking as well. However, mixing premium and regular unleaded gas is usually not necessary as most gas stations sell mid-grade gas at a relative price. Mixing premium and regular unleaded gas may not provide a huge benefit in cost or performance, but it doesn’t damage the bike either.

Various gas types at a gas pump with recommendations for each.
The various gasoline types that are likely available at your local gas station. Don’t forget to mix in the appropriate amount of oil with the gas if you have a 2-stroke!

What Gas SHOULD You Use in Your Dirtbike

When you buy a dirt bike, one of the most important things to know is what type of fuel it requires. This information is usually printed somewhere on the bike. On many models, the recommended octane rating appears on a sticker on the fuel tank.

Although many riders like to use high-octane fuel (90 or above) most dirt bikes can get by with 87 or 89 octane gas as well. Four-stroke engines can generally use 87 fuel without any problems, but two-stroke engines usually require a high octane mix because they have a higher risk of detonation.

The user’s manual should include additional information about which octane rating to use in your specific bike. You can also research your specific bike model online to pull up its specifications. 

TIP: If you can’t find information regarding the type of gas to use in your dirt bike, locate the 17-character vehicle identification number (VIN) and plug it into the database located at Vinvaquero.com.

When to Drain and Replace the Gas

  • If you accidentally fill a two-stroke dirt bike engine with unmixed gas, it should be drained and replaced with the correct pre-mixed fuel. Running an engine without any oil in the mix can result in permanent damage.
  • If you accidentally filled your dirt bike gas tank with diesel, it should be drained and replaced with the correct fuel. Running a non-diesel engine with on diesel can cause serious damage to your engine.

When to Run It Anyway

  • If you accidentally put a lower fuel octane gas in your 4-stroke dirt bike it’s usually safe to continue riding as long as you don’t hear knocking from the engine. To avoid knocking it’s probably best not to try to hit high speeds or tackle intense terrain while running on the lower-octane fuel.
  • If you accidentally put a higher octane gas in your dirt bike, you can still run the engine safely. You may have wasted some money on higher-end fuel, but it won’t damage your engine. It may even improve your bike’s performance a bit and reduce the risk of engine knocking.

Final Thoughts

Every one of our dirt bikes needs fuel to operate, that is unless you have one of those fancy electric bikes of course. Although all the octane ratings and the various fuel mixes can seem overwhelming at first, it’s actually fairly straightforward. 

Just make sure you know your dirt bike’s recommended fuel type and stick with it as much as possible. You can add higher octane fuel if you so choose, but don’t go lower than the suggested rating. Doing this will help you avoid engine knocking and a really bad day due to a destroyed engine.

Even if you accidentally add the wrong fuel type, you can always drain it and start over again as long as you catch it before running the bike too long and causing internal damage. Take a deep breath, relax, and work through this problem! Oh, and don’t kick yourself too much for the inattention while filling up, we’ve all done it at some point!

More Helpful Resources

John Hayes

A street biker turned dirt bike rider, I've been riding motorcycles since I was 12-years-old and have a passion for the technical aspects of dirt bike riding.

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