Why does my motorcycle backfire? Explained in detail with fixes!!

Why do motorcycle backfire?
Why do motorcycles backfire?

Motorcycle exhaust sound is a pleasant sound to us riders. But, it becomes annoying when it starts to backfire and create a banging and loud popping or banging sound. A motorcycle backfire is a problem that can damage the engine and reduce its life. So, let’s dive into; what causes a motorcycle to backfire with its solution? Here is what you need to know.

So, Why does my motorcycle backfire? The backfire is caused by the incorrect fuel to air ratio that causes the fuel to burn outside of the combustion chamber. Because of this, you will see flames coming out of your motorcycle exhaust, known as backfire. So, it’s a sign that combustion is happening outside of the combustion chamber.

You will encounter a short-lived flame coming from your motorcycle exhaust in backfiring. There are several reasons for a motorcycle to backfire thus we will be discussing all the reasons below with their solutions. 

Reasons for motorcycle backfire and ways to fix them:-

  • Incorrect Fuel:air ratio
  • Faulty / Dirty Carburetor
  • Bad Spark plug
  • Incompatible aftermarket Exhaust Upgrades
  • Incorrect jetting
  • Poor fuel Grade

Incorrect Fuel to air-ratio

One of the main causes of backfiring in motorcycles is incorrect fuel to air ratio. The air to fuel ratio needs to be correct for the fuel to burn correctly and efficiently in the engine. If the ratio is not correct; because of being too rich or too lean, then it will cause a malfunction in the combustion process in the engine. If you are unsure of the terms; running lean or running rich, it might help.

Engine Running Lean:- It means there is too much air than fuel in the combustion chamber.

Engine Running Rich:- It means the engine is receiving too much fuel and less air combustion chamber.

These situations can occur due to two reasons either your motorcycle carburetor is faulty or the fuel injector is defective.

In both cases your motorcycle can backfire but here are the things you should do to address them. So, here is the problem that a lean and rich mixture can create.

If the engine is running lean then there could be problems with the Inlet valve and Carburetor timing. Here are the tips to troubleshoot these problems.

  • While the motorcycle running lean the engine is receiving more air and less fuel causing the motorcycle to backfire.
  •  For this to resolve you need to do some timing settings to the carburetor. As carburetors are the main component controlling the mix of fuel and air. Thus, by setting the timing on carburetors you can fix the problem of the engine running lean. Here is an article on itstiilruns where everything is discussed in detail step-by-step process to timing the carburetor.
  • Inlet valve primary work is to allow the fresh mix of fuel and air to flow in during the intake and after the process provides the exit for a spent gas during the exhaust stroke. Thus problems with the inlet valve can cause issues with the combustion process that can result in backfire.

Thus, to resolve the issue first check the inlet valve, if it’s causing low fuel entry then address the issue and replace the inlet valve.   

If the engine is running rich there could be problems with carburetor tuning and air filter. Here are the tips to troubleshoot these problems.

  • While the motorcycle running rich the engine is receiving too much fuel and very little air. So, here you should check the air filter, it is the one responsible for providing the required clean air to the combustion chamber. If it’s dirty or clogged you must clean it or, if it’s old replace it with the new air filter.
  • But, when you see the air filter it’s perfectly fine and clean. Then, it’s an indication that something is wrong with the carburetor. For proper fuel mixture, the carburetor tuning should be at its stock setting. But somehow it’s not that’s the reason your motorcycle is running rich. So, it’s time to tune your carburetor to its stock setting. Here is an article from sscycle.com that discusses tuning your carb in detail. Follow along and you will be able to do the job easily.

Faulty / Dirty Carburetor

Dirty Carburetor in motorcycle
Dirty Carburetor in motorcycle

If your bike is backfiring and the motorcycle has a carburetor instead of fuel injection then it’s time to inspect it.

You should be inspecting your carburetor, as it could be the main culprit and cause of the backfiring issues. The carburetor’s job is to maintain the fuel to air ratio and keep it proportional.

If the carburetor gets dirty or clogged then the fuel could not be able to flow through it fluidly causing a lean mixture (less fuel than air) resulting in a backfire.

Thus, make sure to have the carburetor cleaned completely for the fuel to flow smoothly. You should use high-grade carb cleaner to clean the carburetor jets.

Bad Spark plug

faulty spark plug
faulty spark plug

A faulty spark plug can be the reason behind your motorcycle’s backfire and making loud pops. The backfire is caused by the faulty spark plug that produces intermittent spark. When the spark plug isn’t able to ignite the mixture of air and fuel in the engine cylinder then it gets pushed out of the cylinder. So, as soon as it approaches the exhaust header it combusts; producing a loud poop sound which we generally refer to as backfiring.

To troubleshoot the bad spark plug issue you should check the condition of the spark plug. So, check for any burn, smell, bent parts, rust, etc, these problems are an indication of a bad spark plug. The backfiring will be stopped by simply replacing the old spark plug with a new one.

Incompatible aftermarket Exhaust Upgrades

Backfire can also be caused due to incompatible aftermarket exhaust upgrades. There are several reasons; you may have upgraded your exhaust but like sound, performance, etc.

But because OEM exhaust in motorcycles are made to work with standard jetting while aftermarket exhausts are designed to produce more performance and sound. Therefore these aftermarket exhausts sometimes don’t work with the motorcycle standard jetting.

To solve this issue, you should switch to your stock exhaust or you need to jet or tune your motorcycle carburetor to suit your new aftermarket exhaust. The backfiring will be prevented/ stopped due to the proper jetting for the aftermarket exhaust.

Incorrect jetting

Jetting your motorcycle carburetor is one of the dreaded parts of maintenance. Incorrect jetting can affect the carburetor’s ability to mix the air-to-fuel ratio in the right proportion, resulting in backfiring due to the lean or rich mixture. There are some factors that influence carburetor jetting:-

  • Altitudes
  • Weather
  • Upgrades to exhausts

So, if the motorcycle has been jetted for a particular altitude and weather and you ride it to a completely different level of elevation or weather, it can cause the issue of backfire because of the incorrect fuel mixture.

The simplest fix will be to jet the carburetor according to the place where you ride the motorcycle. You can take the motorcycle to the mechanic and get it jetted properly.

Using Low-fuel Grade

High-performance motorcycles require high octane fuel grade to run and provide you the reliable performance. And, if you are using low-fuel grade in your motorcycle either accidentally or by the thought of saving money you are doing wrong that will have its impact.

Using poor fuel grades repeatedly in motorcycles can result in contaminated dirty gas in the motorcycle. It will negatively affect your fuel-injection system causing the motorcycle to backfire.

To solve this issue the only thing you have to do is consider using the fuel grade recommended by the manufactures. If your motorcycle needs high-octane fuel-grade then use it.

Till now we have discussed the 6 problems that could be causing your motorcycle to backfire along with the solution.

Now, there are certain situations when your motorcycle backfires e.g while accelerating or decelerating, or in a startup, etc. In the below section we will be discussing the cause and solutions of backfiring in motorcycles in several situations. 

Causes of Motorcycle Backfire in different situations

There are several situations when a motorcycle backfires. Here are the several situations where a motorcycle backfires can happen:-

  • Motorcycle backfire at startup
  • Motorcycle backfiring on Acceleration
  • Motorcycle backfiring on Deceleration
  • Motorcycle backfiring at high rpm

Motorcycle backfire at startup

If there is unburned fuel/gas in the exhaust then it will result in a backfire due to the hot gas. As soon as you start your motorcycle the unburned fuel will be ignited by the hot gas leaving the engine resulting in a backfire at the startup of the motorcycle.

The reason for unburnt fuel getting into the exhaust is either your motorcycle is running rich at idle or you are using too much choke.

Motorcycle backfiring on Acceleration

The most basic reason for a motorcycle to backfire on acceleration is the inappropriate air to fuel mixture either the mixture is too rich or too lean.

To troubleshoot the lean or rich mixture you should check your carburetor and spark plug. As I have discussed above clogged carburetor and faulty spark plug can cause the mixture to become lean or rich causing the motorcycle to backfire on acceleration.

Apart from this, you should also check the air filter because a clogged or dirty air filter can prevent the flow of air into the carburetor making the fuel to air ratio lean resulting in a backfire. There are other reasons also like incorrect jetting, and poor fuel grade that can cause a backfire in acceleration. 

Motorcycle backfiring on Deceleration

Backfiring is caused by a rich fuel mixture where the combustion chamber fails to ignite the excess fuel. The unburnt fuel gets transferred to the exhaust system when the exhaust port opens. So, when the unburnt fuel of the exhaust ignites it causes a backfire as you slow down (decelerate).

Apart from this, Low compression in the engine can cause the air/fuel mixture to burn slower than the usual rate causing the motorcycle to backfire while decelerating.

Motorcycle backfiring at high rpm

If there is an air leak between the carburetor and the engine then it can cause the motorcycle to backfire at high RPM because of the lean mixture. There are also other reasons for a motorcycle to backfire at high rpm such as clogged carburetors, running rich, using aftermarket exhausts without jetting.

Can a modern fuel-injected motorcycle backfire?

A fuel-injected motorcycle can also backfire due to the emission system malfunction or if an intake leak is present. An intake lean can cause the engine to run lean that can cause the motorcycle to backfire.

Apart from this, the chances of backfire in fuel injection system motorcycles are less frequent compared to the carburetor system because the air-fuel ratio is controlled electronically in the fuel-injected system.

So, if you are running a motorcycle with a fuel-injection system, you should not worry too much about the backfire. The ratio of fuel and air reaching the engine will always be in the right proportion because everything is programmed in the circuit.

Is a backfire bad for your motorcycle?

Yes, Backfirirng is bad for your motorcycle as it can affect the internal temperature of the engine combustion chamber and can cause damage. Backfiring is the result of emission system malfunction where the mixture is either lean or rich. So, by the backfiring, your motorcycle is telling you that something is wrong inside.

Therefore riding with this malfunction is simply not worth it and will harm the motorcycle in long run. I have already mentioned six causes that can cause the motorcycle to backfire with their required solution.

Conclusion

Generally, backfiring issues occur more frequently in carburetor system motorcycles compared to fuel-injected ones. You will see rare backfires in motorcycles having a fuel-injection system.

Many problems could be causing the motorcycle to backfire but I have discussed problems that occur more frequently with its solution. Make sure to not avoid the backfiring even if you like its sound.

Ride hard, ride safe!!

FAQs

What is the difference between Backfire and Afterfire?

According to Wikipedia, A backfire or afterburn is combustion or an explosion produced by a running internal combustion engine that occurs in the exhaust system, rather than inside the combustion chamber.

Nowadays, everyone understands when you say backfire, but if we are going to be accurate in our descriptions, what you call backfiring is actually after firing.

So, there is little or no distinction between these terms because often both the terms refer to the same thing. So, if someday is talking about after firing, you should assume that they may refer to the backfire. And nowadays these both terms are used with no distinction among them.

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