Why Do Harleys Backfire? (Solved & Explained!)

We’ve all heard those deafening popping sounds from a motorcycle or car. It sounds much like a gunshot and draws our attention very quickly.

Motorcycles and cars that make this popping sound seem like they need immediate attention from a mechanic. This is much the same as when you hear someone coughing loudly, and you think they probably need a doctor.

The popping sound you hear from a bike is called backfiring, and a lot of Harley Davidsons exhibit this behavior.

Backfiring can seemingly begin out of nowhere on a Harley and make the owner think twice about taking the bike for a ride.

In this article, we’ll be delving deeper into the backfiring of a Harley Davidson.

Let’s get into it!

What’s The Reason Harleys Backfire?

Harley Davidsons backfire because of a little explosion in the intake or the exhaust. This explosion is supposed to happen in the combustion chamber of the Harley. It is normally due to an interruption in the engine’s operation or exhaust system.

This mini-explosion can be quite scary for a rider and people around the bike. What makes it so scary is that the sound is typically unpredictable and can happen when the bike starts, accelerates, or decelerates.

The emission of a Harley includes the exhaust system and how the bike burns its fuel. When a Harley has something wrong with the emission system or fuel flow, backfiring is most likely to occur.

Backfiring is common on other vehicles, too, because they also have an exhaust or fuel system. A combustion chamber in the vehicle is supposed to contain the explosion and minimize the noise. If it fails to do so, it might be time to check the vehicle at a mechanic or dealership.

The exhaust on a Harley is properly tuned from the factory to function coherently with the engine.

As soon as the third-party part or an upgrade is performed on the Harley, it starts behaving unpredictably. This can be in the form of a misfire when starting the engine or backfiring.

Other Reasons a Harley Might Backfire Include:

  • Failing fuel pumps
  • Incompatible exhaust
  • Low fuel pressure
  • Unbalanced air-to-fuel ratio
  • Exhaust leak
  • Fuel filters are blocked.

These can all indicate a malfunction in the bike’s mechanics and might need to be attended to.

The stock muffler on a Harley is factory-designed to decrease or avoid loud backfiring. If this part and others are replaced, it can throw off the vehicle’s balance and cause backfiring.

Read our article which explains about Do Harley Davidson Motorcycles Leak Oil?

Is Backfiring Bad For A Motorcycle?

Backfiring on a motorcycle is the popping sound of unburnt fuel igniting in the exhaust. This typically happens during deceleration.  While the popping itself may not be harmful, it does indicate that your bike may not be tuned properly, which CAN lead to harmful problems.

Popping on a Harley is not uncommon, and many riders rather enjoy the light popping. When the Harley is backfiring with the stock exhaust system still intact, it might signal the exhaust pipe weakening or the muffler is malfunctioning.

During backfires, unburnt fuel goes out through the exhaust valve on deceleration. The fuel ignites and causes the popping sound.

Although backfiring isn’t all that bad for a bike, it can cause other problems. When in a confined space, the backfiring can damage hearing. Excessive backfiring can also emit small flames from the exhaust, which can cause a fire.

Many of the Harley-Davidson’s that have excessive backfiring have bad mileage because the fuel is being wasted.

The fuel is supposed to be ignited inside the bike’s combustion chamber. In the case of a backfire, the fuel ignites outside the bike’s exhaust, and this fuel is wasted.

Backfiring on deceleration and speeding should not cause any bad effects on the bike. This is on the assumption that everything else on the bike is running well.

How Do You Get Your Harley To Backfire On Purpose?

The most common way to intentionally cause a backfire on a Harley Davidson is to replace the exhaust system with aftermarket parts. Another popular way among bikers is to rev the engine and then turn the ignition back on. Backfiring intentionally can lead to bent valves and blown exhausts.

Even though intentional backfires are frowned upon by bikers, they can be amusing for other people. Intentional backfiring should not be performed as it can cause damage the bike, such as bending the bike’s valves or blowing exhaust gaskets.

The stock muffler and exhaust on a Harley Davidson are tuned in such a way as to decrease the sound and effects of a backfire. An aftermarket exhaust can let more air into the bike’s intake, leading to more audible backfiring.

Another common practice to cause a backfire is riding the bike in gear to revs upwards of 3,500RPM. The ignition is then turned off and then on again with the throttle turned all the way up.

Revving the bike high then turning it off fills the exhaust canisters with fuel. When the ignition is switched back on, the fuel and hot gases are ignited, and the explosion or backfire occurs. This has to be done with some timing because backfiring is unpredictable.

When done excessively, this can lead to bent valves and a blown apart exhaust pipe. The noise can get so loud that it can damage other people’s hearing and scare them because some backfiring noises sound like gunfire.

What Causes Backfire On Deceleration And Acceleration?

Backfire on deceleration or acceleration on a Harley Davidson is due to the burning of excess fuel in the carburetor’s intake port. A lean air or fuel mixture from the carburetor of a Harley Davidson results from drastic changes in the pressure.

Backfiring during acceleration typically signifies air in the intake system of a Harley Davidson. This means the system has developed an air leak, which results in extra air going in the engine. The extra air unbalances your engine leading to backfires.

On the other hand, backfiring is simply burning off of the excess fuel that is unused during combustion. This sound is normally from the exhaust, and it signifies a faulty combustion process.

What happens is that when the exhaust ports are opened, there’s too much fuel for the combustion chamber to have burnt. This leads to left-over fuel being ignited after the combustion process has already taken place.

Most Harley Davidsons will have backfire upon deceleration because the engine has lost some compression. Low compression means that the Harley cannot burn the fuel faster than the air, and the fuel mixture is coming into the combustion chamber.

Other Causes of Backfire During Acceleration and Deceleration:

  • Bad ignition system wiring
  • The Harleys engine timing is bad.
  • Low compression in the carburetor
  • Failing valve spring

All these causes can sometimes be fixed by simply adjusting the timing on the Harley Davidson. If it looks like the backfiring is not decreasing or becoming louder, it might be sorted by a mechanic.

What Is Wrong If My Harley Backfires Too Much?

Excessive Backfiring on a Harley Davidson is typically restricted air and fuel flow. The best way to avoid excessive backfiring on a Harley Davidson is the regular maintenance of the bike. Regular maintenance includes cleaning the carburetor and the fuel injector nozzles. A lower-grade fuel may also result in excessive backfiring on a Harley.

Extreme cases of backfiring on a Harley Davidson usually indicate a bad balance between the engine’s air and fuel flow. Another culprit of excessive backfiring on the Harley points to bad spark plugs.

Overused spark plugs may show a darker color, such as black or dark brown, meaning they will likely fail and need to be replaced. On a Harley Davidson, you may also need to check the spark plug wires and the ignition coil.

Problems that are spark plug and ignition related are also when the bike backfires only at specific times.

This means the bike only backfires when turning or decelerating into a corner or to a stop.

Do Harleys Backfire Through The Exhaust System?

Harley Davidsons typically dump excess fuel out the exhaust valve and end up combusting in the exhaust pipe, causing the backfiring. If the Harley Davidson emits flames out the exhaust, a yellow flame means the bike runs rich, whereas blue flames mean the bike is running lean.

When it comes to backfiring on deceleration, the bike typically backfires through the exhaust pipes. In the event of a backfire when accelerating, the Harley backfires through the motorcycle’s combustion chamber.

The combustion chamber and the exhaust pipes and wiring are all part of a Harley Davidson exhaust system. This means that if any of the system’s parts are malfunctioning, the whole exhaust system will be unbalanced.

The popping sound when backfiring gets louder when aftermarket exhaust pipes or other parts are installed. This introduces an imbalance in the exhaust system and leads to more backfiring.

Most owners are advised to get the Harley Davidson re-tuned and re-jetted, especially after changing any exhaust system parts.

A professional re-tuning and proper engine timing can get the exhaust back into balance and reduce backfires.

Depending on the type of exhaust, getting a good air cleaner and fuel controller may reduce or eliminate the backfiring.

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