Is Motorcycle Backfire Bad? Here Is What You Need To Know

Motorcycle Exhaust

Motorcycle backfiring can be annoying since it produces such a huge popping noise. Not to mention, you sometimes loose power while riding the bike.

So, is motorcycle backfire bad? A motorcycle backfire is inherently bad since unburnt fuel is detonating in a mistimed manner. The loss of fuel results in loss of power and low mileage for the motorcycle. In addition, the fuel detonation causes overheating of the engine and the exhaust.

In addition, backfiring produces huge popping sound which can be annoying, especially if you live in a peaceful neighborhood.

Before diving into the solutions for backfiring, Let’s look into – what does a backfire mean and the reasons for backfire.

What Is Motorcycle Backfire?

Motorcycle backfiring is the mistimed detonation of unburnt fuel anywhere between the combustion chamber to the exhaust.

Most commonly, this detonation takes place in the exhaust once the unburnt fuel comes in contact with the hot air in exhaust system.

This detonation of the fuel will create a large popping sound, thus, creating a backfire noise. You can easily identify whenever your motorcycle backfires simply from the sound of it.

The backfiring is usually caused by either a rich or a lean air fuel mixture entering the engine combustion chamber. The incorrect air-fuel mix ratio results in a portion of fuel not burnt.

This unburnt fuel will detonate in a mistimed manner somewhere along its path from the combustion chamber to the exhaust, thus causing backfire.

Is Backfire Bad For A Motorcycle?

A motorcycle backfire is inherently bad since unburnt fuel is detonating in a mistimed manner and mostly outside the engine. The loss of fuel results in loss of power and low mileage for the motorcycle. In addition, the fuel detonation causes overheating of the engine and the exhaust.

Also, the rich or lean air-fuel mixture which causes the fuel to get unburnt in the engine combustion chamber, will lead to engine overheating.

And when this unburnt fuel finally burns in the exhaust system after it comes in contact with hot air, the detonation release heat in the exhaust. Thus, overheating the exhaust pipe.

If the exhaust pipe overheats continuously, it forms an oxidized layer on the pipe – resulting in bluing or coloring of the exhaust pipe.

Another problem of motorcycle backfiring is the noise it produces. The exhaust popping sound can be annoying and if you live in a peaceful neighborhood, get ready for some irate neighbors cursing you for that backfiring noise.

Reasons For Motorcycle Backfiring

Now that we know what a motorcycle backfire means and what are the problems backfiring leads to, let us look into the reasons for backfiring.

The main causes for motorcycle backfire are as follows.

  1. Rich Air-Fuel Mixture
  2. Lean Air-Fuel Mixture
  3. Masked Spark Plug
  4. High Flowing Exhaust
  5. Clogged Jets
  6. Dirt In Carburetor

Let us discuss each of these reasons one by one.

#1 Rich Air-Fuel Mixture

Rich air-fuel mixture refers to a high proportion of fuel amount with respect to the air present in the mixture.

When a rich air-fuel mixture enters the engine from the carburetor, the fuel will not burn completely. The excess fuel amount which remained unburnt, will go to the exhaust and detonate there once it finds high temperature air there. This detonation is what causes exhaust backfiring in the motorcycle.

Solution

If rich air-fuel mixture is the reason why your motorcycle is backfiring, you need to check two things:

  1. Check if air filter is clogged
  2. Carburetor tuning

A fuel rich mixture can either because of restricted air entry due to clogged air filter or carburetor adding more fuel to the mixture.

If the air filter is clogged and dirty, clean it or much better, replace it with a new one. If it is the carburetor, readjust its tuning.

#2 Lean Air-Fuel Mixture

Lean air-fuel mixture in the engine is the exact opposite case of a rich air-fuel mixture.

In a lean air-fuel mixture, the air amount will be much higher in proportion to the fuel amount present.

In a rich air-fuel mixture, fuel amount will be in excess and in a lean air-fuel mixture, air will be in excess amounts.

When there is too much air in the engine, the fuel gets clouded by the air in the combustion chamber and as a result, does not get burned completely in the engine.

This unburnt fuel when reaches the exhaust will then detonate to cause backfiring in the motorcycle.

Solution

Whenever a lean air-fuel mixture is causing problems in your bike, you need to look into these two things:

  1. Carburetor tuning
  2. Inlet valve

Check both the carburetor as well as the inlet valve which is causing low fuel entry into the engine. Once the issue is addressed, the motorcycle backfiring will stop automatically.

#3 Masked Spark Plug

Spark plugs are important engine components used to ignite the compressed air-fuel mixture in the combustion chamber.

But spark plugs can be subjected to deposit formations.

If there are deposits formed on the spark plug layer, then it would be difficult for the plug to ignite the engine. The deposits block the spark plug to generate spark in the combustion chamber.

As a result, a masked spark plug can cause uneven ignition inside the combustion chamber, with most of the fuel leaving the engine unburnt.

This unburnt fuel, upon reaching the exhaust pipe, will detonate – to cause motorcycle backfiring.

Solution

Spark plugs need to be checked every 4000 to 5000 miles of distance traveled.

You need to keep the spark plugs in good condition by checking it regularly during every motorcycle servicing.

If a masked spark plug is the problem and is causing backfire, then you might have to replace the spark plug entirely.

To determine whether you need to replace the spark plug or not, check the spark plug gap using a wire type feeler gauge.

The spark plug gap should fall within the tolerance limits specified by the manufacturer. Typically, around 0.03 – 0.04 inches (0.8 – 0.9 mm). If the gap is less than the tolerance limits, you have to replace the spark plug with a new one.

#4 High Flowing Exhaust

Another reason why your motorcycle backfires is because it has 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 backfiring, i.e. exhaust backfire 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.

On a high flowing exhaust system, where air can enter the exhaust easily, a high amount of decel backfiring can be experienced in the motorcycles.

Solution

If the backfiring is because of high flowing exhaust in your motorcycle, you need not worry much.

There won’t be any damages associated with backfiring caused due to high flowing exhaust pipe. There will be noise though, but that’s it.

If at all you want to address it, you can replace the exhaust pipe with a large one. Again, this is not at all required.

#5 Clogged Jets

Carburetor and Jets

Clogged jets are another reason why your motorcycle is backfiring.

Dirt accumulation in the jets will prevent sufficient fuel flow in the carburetor. This in turn will lead to a lean air-fuel mixture entering into the combustion chamber.

And as discussed above, a lean air-fuel mixture will result in your motorcycle backfiring.

So, dirt in the jets – pilot jet, main jet and needle jet – in any of these, will ultimately lead to backfiring.

Solution

The solution to clogged jets is straightforward. You need to clean up the dirt accumulated in these jets.

You might have to remove the carburetor as well to clean the clogged jets. Which brings us to our next and last point.

#6 Dirt In Carburetor

Carburetor

Any dirt in the carburetor will affect the air-fuel mixture ratio entering the combustion chamber.

Carburetor is the components that mixes air and fuel, and then transfers the mixture to the engine for combustion. If there is dirt in the carburetor, the fuel and air proportion will not be right entering the engine.

As a result, the fuel flow will be disrupted, resulting in either a rich air-fuel mixture, or a lean one. Either case, as discussed above, will cause backfiring.

Solution

It is always advised to clean the carburetor once every year to maintain the carburetor in its optimum working condition.

To address the backfiring problem, the dirt in the carburetor should be cleaned. For preventive maintenance, a cleaning frequency of one year should be sufficient to keep the carburetor clean and running in a good condition.

How To Fix Backfire On Motorcycle

Once you know the cause of backfiring in your motorcycle, it is time to address the cause to fix the backfire.

Based on the reasons for backfiring, here are the solutions you can undertake to address the backfiring problem in your motorcycle.

  • Tune the carburetor: To address problems of rich or lean air-fuel mixtures going from the carburetor to the combustion chamber, you need to tune the carburetor. For preventive maintenance, tune the carburetor every 6 months at least. Or ask for carburetor tuning every time you take your motorcycle for servicing.
  • Check the air filter: Clogged or dirt in the air filter will prevent air flow into the system. Check the air filter for dirt, and if the filter is blackened or has too much dirt clogged – you have to replace the air filter entirely.
  • Clean the jets and carburetor: If dirt in the jets and carburetor is what causing the backfire, then you need to take out the carb from your bike and clean it along with the jets. For preventive care, clean the carburetor at least once in a year.
  • Examine spark plugs and replace, if necessary: Check the spark plugs for carbon deposits. A masked spark plug not only causes backfiring, but also affects engine power and mileage drastically. If the spark plug gap is not within the limits, it is better to replace it with a new one.
  • Add/change muffler: This not necessarily required. However, if the backfiring is because of a high flowing exhaust and are too much irritated by the backfiring noise, then you can consider adding or replacing the muffler or even the entire exhaust pipe. Again, this is not at all required.

Difference between Backfire vs. Afterfire

Backfire and afterfire are often used interchangeably with little to no distinction.

While backfire is the mistimed burning of fuel anywhere from the engine cylinder to the exhaust, afterfire refers to the fuel detonation in the exhaust.

In other words, we can say, afterfire is a subset and a form of backfire.

However, more often than not, these two terms are used interchangeably and are deemed to refer the same.

So, next time when someone mentions afterfire, assume that they are referring to backfire. In modern motorcycle terminology, both backfire and afterfire – are used with no distinction between them.

Conclusion

As discussed, motorcycle backfire is when the fuel is unburnt in the engine and is then detonated in a mistimed manner outside the engine, thus causing loud popping sounds.

Backfire can be harmful to a motorcycle since it starves power to the motorcycle and also reduces mileage. In addition, backfiring also leads to engine and exhaust overheating.

The noise generated from backfire can be annoying as well, especially if you live in a peaceful neighborhood.

The main reasons for motorcycle backfire include – rich or lean air-fuel mixture, masked spark plugs, high flowing exhaust, clogged jets or dirt in the carburetor.

To address the backfiring issue in your bike, you need to – tune the carburetor, check the air filter, inspect the spark plug, and clean the carburetor and jets. You might have to replace the air filter and/or spark plugs, if necessary.

Once you have addressed the issue, your motorcycle is good to go without any backfiring noise.