Why Does My Dirt Bike Backfire [All Possible Reasons]

It’s a bright morning, and you’ve got your bike running and ready to hit the trails. But you suddenly hear a loud pop sound, and you’re worried. It’s the sound of your dirt bike backfiring, so you quickly Google why! 

If you don’t have much experience with motorcycles, your dirtbike backfiring can be scary. But although it’s fairly common, a backfiring engine can be problematic. 

I’ve owned dirt bikes since I was 17, and I’ve seen my engine backfire several times. In this article, I’ll explain why your dirt bike backfires and show you all the tricks I’ve learned over the years to deal with the issue. 

Why Does My Dirtbike Backfire?

Dirt bikes backfire when the bike’s emission system malfunctions. This can happen when there’s an incorrect ratio of fuel to air which causes incomplete combustion. There’s either too much fuel and not enough air or too much air and not enough fuel. 

Like most motorcycles, dirt bikes backfire when there’s an explosion in the form of a loud popping sound from the intake system or exhaust. In a healthy engine, fuel combusts within the engine’s cylinder while the compression cycle is ongoing. However, an emission system malfunction can cause another combustion to occur outside the engine’s cylinder, which leads to a dirt bike backfire. 

Let’s take a closer look at the two main reasons why your emission system is malfunctioning:

Engine Running Rich

We say an engine is running rich when there is too much fuel and not enough air. A dirt bike engine needs the right ratio of fuel to air mixture for efficient combustion to occur.

In older bikes, the ratio of fuel to air was set in carburetors by the manufacturer. However, modern bikes now have their air-fuel ratio set in the engine control unit, which gives a more accurate measurement.

When there’s more fuel than air, the excess fuel will enter the exhaust pipe and combust immediately; it reacts with combustible oxygen. This manifests as a loud banging sound. You can also use a fuel stabilizer for that.

An engine running rich will cause low gas mileage and could damage the bike’s internal engines. It is easily detectable due to a strong gasoline smell even when the bike is not running. 

Engine Running Lean 

An engine is said to be running lean when the fuel-to-air ratio is such that there’s insufficient fuel and too much air in the combustion chamber. This problem usually happens after you change the air filter. When you replace it with a new air filter that allows a lot of air into the cylinder, it causes a fuel-air imbalance which leads to incomplete combustion. 

The excess air and unburned fuel will move to the exhaust, where they react and manifest as a loud explosion. An engine that’s running lean is an issue that needs urgent attention. 

A lean engine translates into a slow combustion rate. This means more energy is converted into heat rather than mechanical work. It causes the engine to have less power, and acceleration becomes slower. 

Dirt Bike backfiring: How to Fix (With steps)

To fix a dirt bike backfire, you must address the root cause of the problem. There are several factors responsible for an engine backfiring. In this section, I’ll address some problems and how to solve them.

Installing an Aftermarket Exhaust

The exhaust on your bike is specially designed with the right length, elevation, and inner cavity girth. So when you replace it with an aftermarket exhaust that’s not the right fit, you may have an issue with the engine running lean or rich. If your stock exhaust replacement is longer, the engine runs lean, and when it’s shorter, it runs rich. 

How to Fix it

The best way to fix this problem is to correct the air-fuel ratio in your ECU or Carb after you change your exhaust pipe. To do this, you need to remap your ECU if you own a modern bike or re-jet your carburetor if you own an older bike. 

Remapping your ECU involves flashing the bike’s brain. You’ll need to reprogram it to accept new specifications. 

These new settings will replace the stock settings installed by the bike’s manufacturer and allow you to use your aftermarket exhaust without any issues. Remapping your ECU requires skill and experience; you should leave it to an expert technician to fix it. 

Follow the steps below to re-jet your carburetor:

Step 1: Drain the Carburetor

• Shut off your petcock to stop gas from the tank from flowing to the carburetor. 
• Unscrew your drain plug and drain the gas into a pan

Step 2: Remove Carburetor

• This process is unique for every motorcycle. Hence, you should refer to your owner’s manual and follow the steps provided 

Step 3: Remove Hose

• Remove the carburetor hoses on your engine, and the carburetor should completely come off. 

Step 4: Choose the Right Jet Size

• You can refer to your owner’s manual to see the stock jet size.
• If your engine is running lean, you need a bigger jet number which comes with a larger hole and can accommodate more fuel. 
• If your engine is running rich, you need a lower jet number with a smaller hole and less fuel. 

Step 5: Replace the Jets

• Loosen the screws on the carburetor float bowl and remove the bowl and gasket. 
• After removing the float bowl, you’ll see the main and pilot jet placed at the center of the carburetor. 
• Unscrew the main and pilot jets and replace them with new jets. 
• After installing the new jets, close your carburetor. 

Step 6: Adjust Jet Clip

• To access the jet clip, you need to locate the needle. Remove your carburetor’s diaphragm, top cap, and spring to access the jet needle. 
• Push the jet needle from the way to find the jet clip. You’ll find it attached to the notches. 
• Adjust the clip according to the problem you’re trying to fix. Move your jet clip one rung down the needle if you’re running lean. If the engine is running rich, move the clip up one rung toward the top of your needle. 
• When you’re done, move the needle back into the diaphragm and reassemble your carburetor. 

Step 7: Reinstall Carburetor and Hose

• Using your owner’s manual, reinstall your carburetor and hose correctly. 

Step 8: Test

• Take your bike out for a test ride. If you have installed the correct jet size, you will no longer hear the loud engine backfire sound. 

Dirty Carburetor

If you own an older bike with carburetors instead of ECUs, your bike may backfire due to a dirty or bad carburetor. When the bike sits idle for a long period, the carburetor may accumulate dirt and debris, which causes impurities. 

If the carburetor’s jets are clogged due to dirt, there’s a reduction in fuel delivery which causes the engine to run lean. This may lead to incomplete combustion, which causes the engine to backfire. 

How to Fix it

You can clean a dirty carburetor with the steps below. But first, you’ll need the following tools:

• Safety gloves
• Safety glasses
• Wrench
• Carburetor cleaner
• Rags
• Socket wrench
• Small screwdriver

Step 1: Drain the Carburetor

• Turn off your petcock to stop gas from the tank from flowing to the carburetor. 
• Unscrew your drain plug and drain the gas into a pan

Step 2: Remove Carburetor

• This process is unique for every motorcycle. Hence, you should refer to your owner’s manual and follow the steps provided 

Step 3: Clean or Replace Jets

• Loosen the screws on the carburetor float bowl and remove the bowl and gasket. 
• After removing the float bowl, you should see the main and pilot jets at the center of the carburetor. 
• Unscrew the jets and inspect them to see if they’re clogged, then clean them thoroughly using carb cleaner.
• Alternatively, you can install new jets. 

Step 4: Clean the Float Bowl

• Clean the float bowl using a rag and carburetor cleaner. You should also clean the other parts of the carburetor using the cleaner.

Step 5: Flush out the Holes on the Carburetor

• There are several holes in your carburetor. You need to clean them using the top brand carburetor cleaner, then use compressed air to blow through them. This should clean out the dirt particles in them. Your safety glasses will prevent dirt or fluid from getting into your eyes. 

Step 6: Reinstall your Carburetor

• After cleaning your carburetor, reinstall it using the instructions in your owner’s manual. 
• Your engine should start working perfectly when you turn it on. 

Bad Fuel Pump

Another problem that can cause engine backfiring is a bad fuel pump. When your fuel pump is faulty, it may deliver more or less fuel than is required.

If it delivers more fuel, a running-rich situation can occur. The excess fuel escapes into the exhaust, which reacts with combustible oxygen and causes a loud banging sound. Meanwhile, if the fuel pump delivers less fuel, the engine runs lean, which also causes a backfire. 

How to fix it

Fuel pumps are expensive, so you’ll need to service them regularly so that they remain in good shape for as long as possible. You should also inspect the fuel line and injection while servicing your pump to ensure they’re in good condition. 

Intermittent Spark

This is possibly one of the most annoying reasons your dirt bike backfires because it can be difficult to diagnose. Normally, spark plugs cause the fuel-air mixture in your engine to ignite. The timing of the ignition needs to be precise for proper engine performance. 

However, a faulty spark plug may misfire or not ignite at all. When this happens, the faulty spark plug causes unburned fuel to escape from the cylinder. If the fuel reacts with combustible oxygen, it can cause the engine to backfire. 

How to Fix

You may need to conduct routine maintenance to diagnose spark plug issues. It can be fixed by cleaning the spark plug or changing it completely when it’s discovered. Follow the steps below to fix your faulty spark plug. 

• Step 1: Disconnect the plug lead and clean the areas around the plug. 
• Step 2: Use a spark plug socket to remove the spark plug.
• Step 3: Use a spray plug cleaner and wire brush to clean the deposits from the plug.
• Step 4: Check the spark plug to see if any electrodes are burnt, or the porcelain is cracked. If you notice any, then it’s time to change the plug. 
• Step 5: Check and adjust the spark plug gaps.
• Step 6: Reinstall the plug and reattach the plug lead. 
• Step 7: Start your engine to test if it’s working fine. 

FAQs

Final Thoughts

For many riders, a dirt bike backfire is a common problem that does not always require immediate attention. But several factors could lead to your engine backfiring, and some of the underlying issues may cause serious damage to your engine

Hence, you need to thoroughly check your engine to diagnose the problem and fix it quickly. Alternatively, you may take your bike to your local mechanic to diagnose and repair the issue.