Why Does My Dirt Bike Backfire? – 5 Reasons & How to Fix

Written by

James Stevens

Fact-checked by

Robert A. Verdin

why does my dirt bike backfire

There are various reasons why your dirt bike might backfire. So if you’re wondering why does my dirt bike backfire, it’s not a cause of concern yet until you narrow down the actual cause.

For the most part, a dirt bike backfires due to incomplete combustion resulting from incorrect fuel and air mixture. It typically happens on a 4-stroke dirt bike, but it can also occur on a 2-stroke variant.

But as mentioned, it can be due to other reasons as well.

Most Common Causes of Dirt Bike Backfire


There are several causes that explain why your dirt bike is backfiring when trying to start it. Let’s look at the five most common ones:

1. Too Much Fuel


As mentioned, the common cause for a dirt bike backfiring and not starting is an incorrect mixture of fuel and air. As such, if there’s too much fuel on your bike, you can expect it to backfire.

In order for a motor engine to start, it should have the right fuel and air ratio to initiate proper combustion via the combustion chamber.

If the ratio leans toward more fuel than air (referred to as running rich), it will result in inefficient combustion. This causes excess fuel in small engine to escape via the exhaust pipe, and as soon as it makes contact with oxygen, it will then combust.

In other words, it burns too much fuel than it normally should.

This is the reason why you’ll hear a loud bang. You’ll be able to tell if your bike is running rich by checking the spark plug if it turns dark.

2. Too Little Fuel


On the other hand, little fuel in the cylinders (referred to as running lean) will lead to incomplete combustion. This happens when too much air enters the cylinder than your bike’s manufacturer prescribes.

Contrary to running rich, you can tell if your bike is running lean if the spark plug is a bit whitish. It also requires immediate attention, as running your bike lean can damage its components.

3. Dirty Carburetor


Your dirt bike’s carburetor backfires if it has accumulated too much dirt and debris. Keep in mind that the carburetor is responsible for combining air and fuel in your bike’s combustion chamber.

In a sense, it’s also why your engine might run rich or lean.

Over time, dirt and debris will accumulate in your dirt bike’s carburetor, especially if it’s left idle for a while. This buildup will significantly affect the performance of your engine and even cause backfire through carb to become more common.

4. Poor Compression


Poor compression is yet another common cause for backfiring on deceleration or acceleration. Since it’s responsible for driving the piston in the combustion chamber, the lack of proper compression means the spark plug won’t be able to ignite the air and fuel inside.

In most cases, a leak in the exhaust valve leads to poor compression.

5. Faulty Spark Plug


The spark plug basically ignites the fuel-air mixture inside the combustion chamber. If it’s not working properly, then it will ignite the unburned fuel which leads to loss of power and backfiring.

Diagnosing the Cause of Backfiring


Now that we know the main causes of engine backfiring in your dirt bike, let’s now talk about how you can diagnose them.

Ideally, you need to figure out the specific backfire causes in your dirt bike before you can start to diagnose them.

Once you’re able to determine the root cause, you can then start to fix the issue in order to prevent backfires from reoccurring in the future. That said, here are some common backfire solutions you can follow:

1. Clean Your Bike’s Carburetor


First, check if your bike’s carburetor is clogged and dirty. If it is, make sure to clean it as well as the air duct that leads to it thoroughly by using a carburetor cleaner.

Don’t forget to remove the housing as well.

2. Use the Right Fuel to Air Ratio

Credit: Youtube.com

Regardless if your engine is running rich or lean, you need to follow the same fuel-to-air ratio that’s prescribed by your dirt bike’s manufacturer.

Also, try to use high-quality fuel to minimize any gasoline buildup which can potentially clog your dirt bike’s engine over time. You can get some recommendations from your bike’s manufacturer based on its build and model.

3. Check and Replace the Spark Plug


If the spark plug is the root cause of why your dirt bike is popping on deceleration or acceleration, you want to check its condition first.

If it’s fouled due to carbon or oil buildup, make sure to clean it first. However, once you notice that it’s already worn out, your best option is to replace it entirely.

You should also check the gap between your spark plug and see if it’s either too wide or too narrow. An incorrect gap can affect the performance of the spark plug which leads to backfiring.

Frequently Asked Questions


Is it normal if my bike backfires but won’t start?

Yes, but only to a certain degree. If the reason for the backfire is the engine is running rich or lean, then it could lead to either reduced gas mileage or a slower combustion rate. Either case should require immediate attention.

Can a faulty spark plug cause my bike to run rich or lean?

Not at all. There’s zero connection between your bike’s spark plug and the fuel and air mixture inside the combustion chamber.

How do I know if my bike is running lean?

Running your bike lean can lead to a slower combustion rate. You’ll be able to tell if it’s currently running lean if you notice weird smells, overheating, lack of power, or backfiring via the intake.


Now you know the answer to the “why does my dirt bike backfire” dilemma.

Since there are several factors that can lead to your dirt bike backfiring, you need to diagnose and identify the root cause first before you apply the appropriate solution.

Just keep in mind that while backfiring might not necessarily be a major issue, it still pays to inspect your bike closely, especially if the underlying problem is due to an incorrect fuel and air mixture.

5/5 - (3 votes)

James Stevens

James Stevens is an expert bike mechanic who knows everything from basic repairs to custom modifications. What sets him apart is his ability to explain complex concepts in a way that's easy to understand. Check out his content on Speedway if you need help with upgrades or modifications for your bike.