What Causes a Motorcycle to Backfire?


We’ve all heard a motorcycle backfiring. It is a loud bang that makes everyone around you jump and look. But a motorcycle backfire is nothing more than a small explosion in your exhaust system. Sometimes it happens in the intake system.

It usually means is that there your engine is running too rich, or too lean. This doesn’t allow the combustion process to burn thoroughly and a small backfire occurs.

In this article I’ll talk about the different issues that cause backfiring, and explain what you can do to prevent it.

What causes a motorcycle to backfire?

A motorcycle backfire is caused by a mismanaged air to fuel ratio in the engine of your motorcycle. Anything that interferes with that delicate balance between too much fuel (running rich) and too much air (running lean), can be considered a cause of backfiring.

One cause for motorcycle backfires is replacing your stock exhaust with an aftermarket exhaust pipe. When you do that, you interrupt the way the motorcycle’s engine is set to run by the manufacturer.

The change to a custom exhaust system changes the airflow and causes an imbalance in the air to fuel ration. You either get too much air or too little air and the combustion process cannot handle the change correctly.

Whenever you change from a stock exhaust, you will need to re-jet your carburetors. This is the process of replacing the jets which control the amount of fuel that is released into the combustion chamber. If you don’t do this step, you’re motorcycle is more likely to sputter and backfire with the custom exhaust system.

Another cause for motorcycle backfires is a bad fuel pump. Your engine is not getting enough fuel and this lack allows for too much air to enter the combustion chamber. In newer motorcycle models, this could be a problem with the fuel injection system.

A third cause for motorcycle backfires is the fuel filter. A clogged filter can restrict the flow of gas into the combustion chamber, leaving too much air to burn the fuel. A clogged fuel filter can also be the reason behind the low gas pressure.

Finally, too much fuel can cause a motorcycle to backfire. If there is any fuel left in the chambers when you shut down your motorcycle, that fuel will burn off, causing a backfire.

Backfiring on Acceleration

If your motorcycle backfires when you accelerate, you may have a problem with your intake system. It is possible that your intake system has developed some air leaks that allow for too much air to enter into your engine.

This extra air does not work well with the way your motorcycle engine has been set up to function and causes combustion problems, resulting in backfires.

Also, you could have a problem with bad wiring. The ignition system wiring may not be hooked up properly and this causes the combustion system to malfunction. Your motorcycle’s engine timing may be altered and allows for a build-up of air or fuel in the combustion system.

Another reason why your motorcycle engine backfires on acceleration is that there may be a problem in your carburetor. Low compression inside the carburetor can cause fuel or air to build up and result in letting your motorcycle backfire.

Additionally, there could be a problem with the valve springs. Then if you have carburetor issues, it may be a sign that your accelerator pump is not function at 100%. When you hear your motorcycle backfire, there can be a variety of problems with your motorcycle’s engine.

Backfiring on Deceleration

Backfires on deceleration is simply the process of burning the excess fuel left the combustion chamber. It normally happens in your exhaust system and there are three reasons for this.

First, is when the exhaust ports open, the change in pressure causes a very lean mixture of fuel and air. The fuel and air are still burning at this time, but very slowly. The open exhaust moves the burning mixture to the exhaust system, where it explodes when the combustion process is over.

Second, a deceleration backfire comes when the fuel and air ratio is not correct. With too much fuel to burn, the combustion chamber fails to ignite it all. When the exhaust ports open, the unburned fuel is transferred to the exhaust system where it ignites. Once it ignites in the exhaust, you get a backfire as you slow down.

The third reason you get a backfire when you decelerate is because you have lost compression in your engine. The low compression cannot burn the fuel at the same rate the air fuel mixture is coming into the combustion chamber.

Once the exhaust ports are open, the slow burning mixture exits the combustion chamber still burning and enters the exhaust system causing a backfire.

All of these types of backfire can happen when you are stopping at a red light too quickly, or idling at the side of the road after you have stopped for a rest from high speed travel.

What is the difference between rich and lean and how does it affect my motorcycle backfiring?

If you’re like me and your motorcycle’s first backfire results in other riders telling you “your bikes too lean”, you’re probably thinking 🤔 what the hell does that mean?

In short, running rich or lean is a way to describe the ratio between fuel and air in your combustion chamber, the below might help:

🤑 Running Rich = Too much fuel, not enough air

💪 Running Lean = Too much air, not enough fuel.

How does running rich affect my motorcycle backfiring?

If your engine is running rich then the lack of air in the combustion chamber will cause a lack of explosion in the combustion chamber. And when you have a combustion engine that misses the explosions necessary to drive the pistons, this leads to excess fuel being passed out through the exhaust. This fuel is heated up by the touch of the exhaust and well… Results in KABOOM!

How does running lean affect my motorcycle backfiring?

If your engine is running lean then the extra air in the combustion chamber will cause a ‘starving’ of fuel in the combustion chamber. This is usually to do with low fuel pressure or a clogged fuel filter. The starving of this fuel in the combustion chamber means that there will still be some excess air and fuel that isn’t used up by the time the exhaust valves open. Resulting in KABOOM!

Is backfiring bad for my motorcycle?

Backfires when rolling onto throttleBackfires when rolling off throttleBackfires when fixed or steady on throttle
Indicates a seriously lean condition which is harmful to your engine.this is just a release of combustible gases and is not harmful to your engine.This is generally due to too tight or burned valves and is harmful to your engine.

Does backfiring mean something needs fixing?

Not necessarily. Sometimes a backfire can be fixed by the simple turn of a mixture screw which changes the air to fuel ratio, and a little adjustment is all you need to clear up the problem. But not all backfires can be fixed this simply.

But, always check the most simple problem first. If it can be fixed with a turn of the screw, you have saved yourself some time and money. If the backfire is not stopped with this quick fix, then you may have to do some motorcycle repair work.

As laid out in the earlier sections, you have to search your engine for any unknown problems. Again, you should start with the easiest and cheapest options first. Check your fuel line to see if there is a lack of pressure and then go to your fuel filter. These items are easy to fix and should not cost you a lot of money.

After that, you move on to your fuel pump to see if it is defective. You might want to check your accelerator pump at this time as well. Finally you should check out your carburetor to see if there is a problem with its internal parts.

Also, check your intake system to see if any air leaks have made their way into that system. All you have to do is fix the defective parts once you find it. Your motorcycle repair should be done logically. Keep in mind that motorcycle backfires are merely a warning that something could possibly be wrong with your motorcycle engine.

How to prevent motorcycles from backfiring?

When it comes to preventing your motorcycle from backfiring make sure that you regularly clean your carburetor, check your fuel filter is clean and clean your jets or fuel nozzles.

There is always a solution to your motorcycle backfiring problem. You do not have to wait till there is an actual problem before you fix it. Some preventive maintenance can save you a lot of money in the future.

There is an old saying, ‘an ounce of prevention is worth a pound of cure’ and that saying does apply to motorcycle backfiring. A little regular maintenance on your motorcycle can go a long way to preventing engine trouble and backfires.

4 tips to prevent your motorcycle from backfiring

  1. Regular cleaning of your carburetor: Regularly cleaning your carburetor will flush out any dirt that restricts both air and fuel flow. A good carburetor cleaning agent should do the trick.
  2. Check your fuel filter: When you check your fuel filter make sure it is clean and able to handle the workload. There is nothing wrong with replacing an old fuel filter before it starts causing problems.
  3. Clean your jets or fuel injector nozzles: If these parts get clogged with dirt, you may have backfire issues. Another good cleaner should do the trick and make your life a little easier.
  4. Use better quality fuel: Another problem that may cause your motorcycle to backfire is the fuel you are using. Lower-grade fuels are not as clean as you think or they do not burn as well as you want. Changing the fuel you use can help maintain your engine and keep it from backfiring.

Some Final Words

Hearing your motorcycle backfire is not the end of the world. You do not have to panic and rush into the motorcycle repair shop and spend lots of money fixing the backfire issue.

All you have to do is remember the causes of backfires and take the appropriate steps to fix those issues. The backfires could be in the intake system or it may be in the exhaust system. A little time on your part should locate the issue and focus your repair work.

Also, a little preventive medicine on your part, which can be as simple as changing the fuel you use, can go a long way to prevent backfires from taking place.

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