What causes flames from motorcycle exhaust? 6 reasons to look for

By Arif

Motorcycle releasing exhaust flames

Ever wondered what causes flames from motorcycle exhaust? Because you have a badass motorcycle! No… certainly there are some serious causes and some show-off causes.

By no means a motorcycle wants to backfire on its own. If you notice it a few times here and there no need to worry. But if it keeps on happening there is a need to pay attention.

In this post, we will discover the reasons that cause a motorcycle to backfire and how you can prevent this situation from repeating again.

What causes flames from motorcycle exhaust?

Motorcycle exhaust is prone to flames when it is low on fuel or when there is too much fuel in the tank.

Motorcycles can also backfire due to faulty carburetors, spark plugs, dirty fuel pumps, and filters.

Some people like to show off their mean machines by creating mesmerizing sounds of vroooom with sparkling displays of backfire. This is possible by using aftermarket exhausts which is also one of the reasons for motorcycle flames.

Whatever way you want to see it or show it, such flames/backfire is a sign of mal-functionality that needs to be looked after and resolved.

Are you running your motorcycle on low fuel?

Low fuel or lean running motorcycle is one of the common factors for backfiring. What does it actually mean?

It means that your motorcycle is running on low fuel and there is more air in the gas tank than required.

Both air and fuel should run according to the balanced ratio of your motorcycle structure. This is normally set by the manufacturer in the engine control units.

In the event of excess air, the fuel enters into the exhaust pipe which causes the spark plugs to ignite this mixture of air and fuel creating a backfire. You will see the spark when you are running your bike at low RPM.

A low fuel instance occurs when you change an air filter with one that has more capacity to flow the air freely. This change may cause clogging in the jets or readjustment of the engine control unit.

As a preventive step, always keep the fuel levels in check and monitor the condition of spark plugs to detect lean instances.

Filling too much fuel

If your motorcycle has excess fuel, it creates a situation opposite to a low-fuel instance. The combustion chamber gets affected with more fuel which cramps the space for air to enter.

Therefore, when the fuel is more and the air is low it unbalances the ratio causing the fuel to get ignited by the heat of the exhaust system. This does not necessarily release a backfire but creates a large bang or a startling sound.

Overfilling the tank can impact the overall fuel mileage of a motorcycle. Not to forget the need to check the carburetor (if it’s an old bike) and the color of the spark plugs.

If the spark plugs are getting darker it is time to check the balance of air and fuel mixture to prevent a backfire. 

Check the carburetor: is it faulty or dirty?

The carburetor is another culprit to give your motorcycle firing jolts. In the events of low fuel and more fuel, this is the most-affected part that remains confused.

Motorcycle faulty carburetor

Because of this confusion, the carburetor makes a motorcycle run lean or rich (low and more fuel situation) and fails to create a balance between air and fuel which causes the engine to misfire.

The misfiring often leads to loud popping sounds and excessive smoke from the exhaust.

To avoid misfiring from the carburetor ensure to clean it regularly using a cleaning kit and adjust the jets to their original settings for better balance.

Motorcycles (especially new ones) may not face the heat from carburetors since they are set with a balanced air-fuel ratio through direct fuel injection and an engine control unit.

So, if you have new model bikes then don’t worry but do follow the process above in the case of older bikes.

Spark plugs not sparking

Motorcycle backfiring is often caused by spark plugs not performing according to their potential.

A number of reasons such as bad timing, worn out or faulty spark plugs, bad quality fuel, and improper gaps in the spark plugs are responsible for creating a deviation between the air-fuel mixture.

Intermittent spark plugs fail to ignite the air and fuel mixture in the combustion chamber. Add to this, mistime firing and sequencing leaves unburnt fuel and loss of power.

This unburnt fuel combusts itself through the exhaust valve generating backfire flames. Secondly, if you notice a lack of acceleration while throttling harder it is a sign that the spark plugs are not responding.

To control misfiring and loss of power situations, do keep a check on spark plugs (their color) and replace them periodically for a better ride.

It is also a best practice to use good quality fuel while riding your motorcycle to keep the spark plugs in good condition for a long time.

Firing on all cylinders with Aftermarket exhaust

So, you don’t like the way your motorcycle exhaust looks or are too crazy to show how your motorcycle sounds and ride.

Motorcycle backfiring

If yes, then you would definitely take a step to install an aftermarket exhaust. But do you know what it can do to your bike?

Aftermarket exhausts are one of the main reasons to out-balance the flow of fuel in the exhaust system.

These exhausts are designed to free flow the fuel which in case of engine running rich can throw the unburnt fuel in the exhaust system to create commanding sounds with backfire.

The sound from the exhaust is mesmerizing to grab attention however, such movement of fuel is not good for the exhaust system in the long run.

It is not recommended to install aftermarket exhausts that are high on design and low on usability.

If the need arises and if you are in a show-off mood always choose the stock exhaust that is properly designed and approved to suit your bike’s model and capabilities.

Deficiencies in the fuel pump and filter

Fuel pumps play an important role in supplying fuel to the engine. It is like circulating the blood to the heart of your vehicle.

If there are deficiencies such as leaks or clogs in the fuel lines the actual fuel may divert to the exhaust system. When this fuel begins to combust, it creates a backfire. Such an instance could take place in both scenarios that are low fuel or more fuel.

A faulty fuel pump or filter causes an incorrect air-fuel ratio which is again a reason to create flames in the exhaust. This may even lead to low pressure of fuel in the cylinders which impacts the acceleration.

As a preventive measure, test the fuel pressure to check the level of fuel flow. In case of abnormalities, replace the fuel pump or filter immediately.

These are the main causes that mostly generate flames from motorcycle exhaust. Some of the other miscellaneous reasons include leakages to the vacuum, and airbox, torn piston rings, fluttered head gaskets, etc. which can create a ruckus inside the exhaust valves.

The best way to tackle these problems is through proper maintenance, riding at a smooth pace, not altering the actual parts of your motorcycle, and more importantly keeping the level of fuel always balanced.

Final thoughts

Creating abrupt noises through motorcycle exhaust is fun riding. It does turn the heads around and make your mean machine stand out in the crowd.

Similarly, exhaust flames or backfiring is not always good. We have found the reasons that cause a motorcycle to backfire.

Most of them are related to human error and glitches in the technical parts associated with the fuel tanks, spark plugs, filters, and obviously exhaust systems.

If not taken care of, frequent backfiring could lead to serious technical faults in your bike which could impact the overall performance. In some cases, it may hamper your ride on the road leading to accidents and physical injuries.

So, stay alert, keep timely checks on the exhaust system, and once in a while always take your motorcycle to a professional for thorough check and maintenance.

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I am the founder of TheCarPlus. As a passionate car owner and enthusiast, I offer practical solutions and insights from my own personal experiences combined with extensive online research.

The purpose of creating this website is to empower fellow car owners and motorcyclists like 'YOU' with knowledge and practical solutions to enhance your vehicle's performance and aesthetics.

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