You might have noticed whenever you accelerate your motorcycle and let off the throttle, your exhaust starts popping and backfires. The bike runs great, idles smooth, but the exhaust pops.
Why do motorcycle exhaust keeps popping? In a high flowing exhaust system, the excessive hot air detonates any unburnt fuel coming to the exhaust. This detonation of the unburnt fuel produces a pop-pop sound, more commonly referred as popping.
Why Exhaust Popping Occurs?
With a high flowing exhaust system, fresh air can be drawn back into the exhaust system. And the unburnt fuel that comes out of the engine to the exhaust, mixes with the higher temperature air in the exhaust system.
And when this unburnt fuel meets the high temperature air, the detonation happens – resulting in a pop-pop sound. More commonly referred as popping.
The popping in the exhaust system is nothing but the unburnt fuel getting burnt. Not in the engine, but in the exhaust system.
Popping happens because of 2 main reasons – i) there is unburnt fuel in the exhaust; and ii) there is an excessive amount of air in the exhaust.
Let us look into both of these reasons one by one in detail.
#1 Unburnt Fuel in the Exhaust
The first case, unburnt fuel is a more common occurrence in carburetted engine than in a fuel injected engine.
This is because, in a fuel injection system, the air-fuel ratio constantly changes depending on the engine requirements. The changes in the ratio are made by the ECU which continuously collects data from various sensors in the motorcycle.
Carburetted motorcycles, on the other hand, does not have such an evolved fuel injection system. The air fuel ratio entirely depends on the tuning of the carburetor fixed by the operator.
So, whenever the rider decelerates the bike suddenly, there is a chance of fuel not getting burnt completely in the combustion chamber.
As a result, a small amount of unburnt fuel will flow to the exhaust system. This is especially applicable when the carburetor tuning is not properly adjusted to the riding conditions.
That’s why, carburetted motorcycles are more prone to popping in the exhaust whenever you decelerate than a motorcycle with fuel injector.
#2 Excessive Air in the Exhaust System
Second, the presence of excessive amounts of air in the exhaust system. This is possible only when you have a high flowing exhaust system. If your motorcycle has a larger opening at the back and a short pipe, then it has high flowing exhaust system.
Decel popping, i.e. exhaust popping during deceleration, is in fact a common phenomenon in motorcycles with high flowing exhaust system. Shorter the length of the exhaust pipe and larger its opening, higher is the air flowing in the exhaust.
Many modern motorcycles have robust mufflers which restrict the entry of air coming from the exhaust opening. These mufflers act as restrictive barricade in letting the air come back into the exhaust system.
But on a high flowing exhaust system, where air can enter the exhaust easily, a high amount of decel popping can be experienced in the motorcycles.
Here is a detailed post on exhaust popping during deceleration.
Does Popping Happens in every Motorcycle?
As touched upon earlier, exhaust popping does not happen in every motorcycle.
This is specifically true for motorcycles with low flowing exhaust systems. When the exhaust pipe has a smaller opening and larger in the length, the air flowing in the exhaust is kept to minimum.
And when the air flowing is minimum in the exhaust, there is no cause for detonation of any unburnt fuel within the exhaust system.
Exhaust popping is most commonly seen in motorcycles with carburetors and hardly occurs in fuel injection systems. As discussed earlier, fuel injection system continuously adjust the air fuel ratio based on the data it receives from various sensors.
For these reasons, motorcycles with fuel injection systems do not face the problem of exhaust popping much.
Also, modern motorcycles have robust mufflers in their exhaust system. These mufflers act as barricades to restrict the air flowing into the exhaust from the pipe opening.
As a result, motorcycles with fuel injectors or low flowing exhaust system or robust mufflers – do not face exhaust popping much in them.
Does Exhaust popping hurt your motorcycle?
When the unburnt fuel in the exhaust reacts with hot air to detonate in the exhaust system, the heat released due to detonation will affect the exhaust pipe overtime.
Exhaust systems have temperature limits as well. They can withstand the temperature of the exhaust gases coming from the engine.
However, too much high temperatures in the exhaust, the exhaust pipes will start feeling the impact. The impact will most commonly be seen in the form of bluing or coloring of the pipe.
The exhaust pipe when subjected to high temperatures, forms an oxidized layer due to the extreme heat. This oxidized layer results in coloring of the exhaust pipes.
The most common color formed is blue. Hence, the term, bluing of exhaust pipes. Apart from blue, the metal pipe can also turn yellow or orange.
Apart from the exhaust pipe coloring in the long term, there is no other material impact because of exhaust popping.
Exhaust popping does not hurt your motorcycle. The only problem of bluing or coloring of the pipe can also be easily taken care.
Another effect of exhaust popping is the noise it produces.
If you live in a peaceful neighbourhood, the loud noise coming from popping might get annoying both to you as well as the neighbours. So, you might want to address this minor inconvenience.
That brings to our next section.
Can we Tune Out the Popping in Motorcycles?
The high pitch popping sound in the exhaust can be annoying to not just the motorcycle rider, but also for the people in the neighbourhood. Many riders prefer to tune out the popping sound.
Except for motorcycles with extremely high flowing exhaust system, the popping sound can be tuned out by adjusting the tuning of the carburetor.
For motorcycles with too high flowing exhaust, their large openings and short pipes allow an excessive amount of air back in the exhaust system. This makes it difficult since any amount of unburnt fuel will detonate and cause the popping.
For other cases, the carburetor can be adjusted to reduce the popping significantly.
To tune the carburetor, note down the speed or rpm at which deceleration popping occurs. Next, dismantle the carburetor from the motorcycle and clean it up.
Once cleaned, tune your carb to optimal air-fuel mixture. Here is a video that guides on carburetor tuning.
Again, it is always better to take the motorcycle to your mechanic or a nearby service shop for carburetor tuning.
Another solution can be, to change the exhaust pipe if the current one is short and has large opening. However, this is not at all recommended since exhaust popping is not a big concern, and replacing exhaust pipe is expensive. Not to mention, other exhaust components need to be adjusted as well.
So, just tune the carburetor to reduce the exhaust popping. No need to go for replacing the exhaust pipes.
In Conclusion
Exhaust popping occurs when unburnt fuel reacts with hot excessive air in a high flowing exhaust system.
Popping does not hurt your motorcycle except for bluing or coloring of the exhaust pipe if persisted for a long time.
To reduce the popping, tune the carburetor for an optimal air-fuel mix ratio. There is no need for replacing the exhaust pipes.
