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Motorcycle Backfire Causes and How to Fix Them

Motorcycle Backfire Causes and How to Fix Them

Sep 15, 2022

Motorcycle backfires are often misunderstood by riders and even mechanics. Many people think a backfire is simply an explosion in the exhaust system, but this isn't always the case. Whether you're experiencing motorcycle backfires on deceleration, acceleration, or braking, it's important to understand the root cause and how you can fix the problem.

We will also cover when you should be worried about a backfire and prevent it from happening.

What Causes a Motorcycle to Backfire?

1. Spark Plugs Not Firing Correctly

The most common cause of a motorcycle backfire is unburned fuel igniting in the exhaust system. This usually happens because the spark plugs are not firing correctly. If your motorcycle's spark plugs are old or degraded, they may not be able to create a strong enough spark to ignite all of the fuel in the cylinders. This can cause unburned fuel to enter the exhaust system and ignite when it comes into contact with the hot exhaust pipes, resulting in a backfire.

2. Incorrect Fuel Mixture

Incorrect fuel mixture also causes motorcycle backfires. If your motorcycle's carburetor is not adjusted correctly, it can result in too much fuel being delivered to the engine. This means that there will be more fuel than can be completely burned, and some of it will end up in the exhaust system. When this unburned fuel ignites in the exhaust pipes, it will cause a backfire.

3. Running Low-Grade Fuel

Another motorcycle backfire cause has to do with the quality of fuel you're using. If you're running low-grade or dirty fuel in your motorcycle, it can cause all sorts of problems, including backfires. Low-quality fuel often contains impurities that can clog up your motorcycle's fuel system, including the carburetor and fuel injectors. These impurities can prevent the fuel from igniting correctly, resulting in backfires and other issues.

4. Dirty Carburetor or Issue with Fuel Injection System

If your motorcycle has a carburetor, it's important to keep it clean. Over time, the carburetor can become clogged with dirt and debris, preventing fuel from being delivered properly to the engine. This can cause all sorts of problems, including backfires. The same is true for motorcycles with fuel injection systems. If the injectors are dirty or there is an issue with the fuel pump, it can cause motorcycle backfires.

5. Electronic Timing Issues

Electronic timing issues also cause backfires. With more motorcycles coming with electronic ignition systems, it's important to be aware of this backfire cause. If the electronic timing is off even a little bit, it can backfire. This is because the spark plugs are firing at the wrong time, which causes unburned fuel to enter the exhaust system and ignite. This could also lead to your motorcycle not starting.

6. Issues With the Exhaust System or Upgrades

Motorcycle owners are always looking for ways to improve performance, and one of the most popular ways to do this is by installing aftermarket exhaust systems or other upgrades. If the exhaust system isn’t installed correctly, however, these modifications could cause your motorcycle to backfire.

7. Bad Fuel Filter

A bad fuel filter can also cause motorcycle backfires. The fuel filter is responsible for keeping impurities out of the fuel, but if it's old or dirty, it can't do its job properly. This means that impurities can get into the fuel and prevent it from igniting correctly, resulting in backfires.

Backfiring on Motorcycle Deceleration

Motorcycle backfires on deceleration are caused by a few different things.

  • When the motorcycle's engine is revved, the mixture of fuel and air in the combustion chamber becomes very lean. When the exhaust port opens, this burning mixture is drawn into the exhaust system, where it explodes.
  • If the fuel-to-air ratio is not correct, unburned fuel can be drawn into the exhaust when the exhaust port opens. This unburned fuel will then ignite in the exhaust, causing a motorcycle backfire.
  • Loss of compression in the engine is also another problem. When the engine's compression is low, it cannot burn the fuel at the same rate as the air-fuel mixture enters the combustion chamber. As a result, when the exhaust system ports are opened, the mixture comes out of the chamber while still burning, entering the exhaust, which causes a backfire.

Backfiring on Motorcycle Acceleration

  • Your intake system may have developed some air leaks that allow too much air to enter your engine, which causes combustion problems and backfires when you accelerate. When there is a lot of extra air in the cylinder, it does not operate well with how your motorcycle engine was designed to function and leads to combustion issues, causing motorcycle backfires.
  • You could have a wiring connection issue with the ignition system, causing combustion system malfunction. Your engine timing may also have been changed, allowing for an accumulation of air or fuel in the combustion system.
  • Another common reason for backfires on acceleration is a problem with the carburetor in your engine. When there's a lot of compression within the carburetor, fuel or air can build up and cause your bike to backfire.
  • The valve springs may also be faulty. If your carburetor is not operating correctly, it might indicate that your accelerator pump isn't working properly. There could be various issues with your motorcycle's engine when you hear it backfire. You should also look out for other engine noises when accelerating too.

Is Backfiring Bad for My Motorcycle?

silver and black cruiser motorcycle parked on the edge of the road

  • If you're experiencing motorcycle backfires when rolling onto the throttle, it means that your bike is running in a seriously lean condition, which can damage your bike. This means you don't have enough fuel in the mixture, causing unburned fuel in the exhaust, which causes the backfire.
  • If you're experiencing backfires when rolling off the throttle, this is likely because of the release of combustion gasses, which isn't harmful to your motorcycle engine.
  • If you're experiencing backfires when steady on the throttle, you could be having burned or tight valves, which is damaging to your engine. This motorcycle backfire cause is often the result of an improper installation of aftermarket parts, such as exhaust systems.

Quick Tips to Prevent Motorcycle Backfires

  • Clean your air and fuel filter regularly
  • Regularly clean your carburetor
  • Check to see if your spark plugs need to be replaced
  • Make sure there is no debris in your fuel tank
  • Ensure your fuel injector nozzles and jets are clean
  • Inspect your exhaust system for any leaks or damage
  • Have a professional tune-up your motorcycle regularly
  • Use the recommended fuel
  • Make sure all your parts fit properly

Learn More About Motorcycle Maintenance

Motorcycle backfire is a common problem that riders face. While it may not always mean there's something wrong with your bike, it's still important to understand the causes and how to fix them. You don't want to find yourself stranded on the side of the road with a motorcycle that won't start. At West End Motorsports, we provide you with comprehensive motorcycle maintenance tips, insights, and guides so you can keep your bike running smoothly.

We also sell top-brand aftermarket parts and accessories for V-twin motorcycle riders, including compatible exhaust systems for Harley-Davidson, Indian, Yamaha. Visit our blog, and browse our upgrades. Have questions about motorcycle backfires on deceleration or acceleration? Contact our industry experts today.