Motorcycle backfire… what a sweet banging and popping sound. It clearly announces that there is a loud-ass bike nearby that should be taken in for service. But why do motorcycles backfires?
Not to worry, I’ll tell you why your bike backfires and how to fix it.
So why motorcycle backfires? Backfire happen when a motorcycle’s quantity of air to fuel ratio is incorrect in the combustion chamber. This creates unburnt fuel leaving the chamber, igniting and exploding inside the exhaust system, creating a backfire.
And this excess fuel burns in the exhaust because you know… fuel ignite at high temperatures… and a motorcycle exhaust is pretty hot.
That is why your exhaust pipe goes berserk, making bang bang, pop pop, and sometimes shooting flame as a cherry on top.
Are Backfires Normal For a Motorcycle?
To a degree, Yes…Backfires are normal for a motorcycle. They often occur when slowing down hard on compression or letting go of the throttle after hard acceleration.
The sound resembles a popping that isn’t particularly louder than regular motorbike engine noise. That is normal and varies from a bike to another.
But the excessive loud noises that resemble the sound of a gun firing and happening repeatedly are not normal. The same is true when flames are shooting out of the exhaust.
If your motorcycle is backfiring during acceleration with notable sputtering of the throttle response and a loss of power, you have a mechanical problem.
But, an aftermarket high-flowing exhaust system is a common ”normal” cause for backfire. Especially when braking on compression.
If your bike has a big pipe opening at the end of the exhaust and a short pipe running towards the end of your bike, it is a high-flowing exhaust system.
It is normal for these exhausts to backfire. They are literary made for that.
Are Backfires Bad For a Motorcycle?
Not immediately, but frequent backfiring causes additional heat and pressure on the engine and exhaust system. Over the medium and long term, backfires will cause premature wear of your exhaust system and some engine components.
If an exhaust pipe overheats, again and again, an oxidized layer will form on the pipe. It will result in blue or brownish staining of the metal over time.
It might even result in the exhaust pipe assembly tearing open in some areas.
Backfires also waste fuel and affect your mile per gallon usage rate. This will reduce the total distance you can ride your bike before you need to fill up.
Also, announcing your presence backfiring around a quiet neighborhood won’t earn you any favor for obvious reasons.
Why Your Motorcycle Backfire and How To Fix it
Here are the most common reasons backfires can happen with your motorcycle and how to fix them.
- Aftermarket or modified exhaust
- Carburator needing adjustement
- Cloged or dirty carburetor
- Dirty injector
- Dirty air filter
- Injector sensor malfunction
- Faulty spark plug
- Damaged valves
Some problems are easy to find and take care of, while some…not so much.
1. Exhaust system
Did your motorcycle start doing backfires soon after you modified your exhaust?
Did you replace your exhaust with an after-market version?
Well, there’s your problem!…probably.
Modifying your stock exhaust can also create a backfire problem.
When a new bike comes out of the factory, its mechanical system will be tuned with its stock exhaust. Change the exhaust, and you broke that mechanical harmony.
How to Stop Carburated Motorcycles Exhaust Popping
To stop backfiring in this situation, you need to retune your motorcycle to the new exhaust.
Your carburetor will need to have its pilot screw controlling the ratio of fuel to air adjusted.
Even then, it might not be enough.
Your motorcycle jets that inject the fuel into the combustion chamber will need a different configuration as well.
How to Stop Fuel-Injected Motorcycles Exhaust Popping
It will be different from a carburated motorcycle since an onboard computer controls your fuel to air ratio.
You need to tell that computer ”hey, differents exhaust now! Please change the fuel and air mix ratio and the way the engine operates.”
You will need another type of computer for that.
This other computer will plug into your onboard computer to modify its programming and how it operates your bike.
Think of it as a software update telling your motorcycle engine how to work from now on properly.
There are two techniques for doing this
- ECU flashing
- Installing a power commander.
I recommend you get a specialized bike shop to assist you at this point if that is the way you’re going.
2. Carburator needing adjustement
Your carburetor needs to be readjusted to its proper fuel to air ratio.
It is a common reason why backfire happens.
Colder temperatures and high terrain elevation might also be causing backfires.
A colder climate will make it harder for your carburetor to do its job properly.
Also at high terrain elevations, there is less air (oxygen).
Depending on your elevation, your motorcycle might not get enough air or too much of it with the carburetor setting it has.
The fix
Find your carburetor pilot adjustment screw.
Refer to the owner and service manual for the proper position the screw needs to be.
Or play around with the screw position until you find where your bike runs how it is supposed to.
3. Dirty carburetor
Pretty much what you think it is.
Your carburetor is dirty on the inside and cant mix fuel and air properly.
The fix
Take apart that dirty carburetor and tell it how much of a bad carburetor it was and give it a good cleaning.
Also, take the time to clean your Jets; they might be clogged and be the actual reason you have backfire.
4. Dirty Injectors
Same as the carburetor, your fuel feeding system is dirty to the point it is not doing its job properly.
Your motorcycle on-board computer will try to cope with the problem. It will be injecting more fuel for better or worse, which might cause backfires.
The fix
You might get lucky
Throw some injector cleaning fluid in your gas tank and full of fresh fuel, and go for a ride.
It could clean the injector and fixes the problem.
But Chances are you need to take your injectors out of your bike and get the fuel system thoroughly cleaned.
5. Dirty air filter
Your air filter might be too dirty to let in the amount of air your motorcycle requires to run properly.
The fix
No rocket science here; get the filter cleaned or install a fresh one.
6. Injector sensor malfunction
The onboard computer of your bike knows how much fuel to inject and at what timing. It knows because it works in synchro with a sensor that tells the computer that information.
When the sensor malfunction, your onboard computer will start to receive a false reading.
Then the wrong amount of fuel will be injected witch can cause a backfire.
The fix
You will have to get that sensor replaced.
7. Faulty spark plug
You need a healthy spark plug to do proper combustion.
A defective spark plug might ”skip” a spark.
Then the fuel that was supposed to be combusted will be flushed in your exhaust and ”explode” there instead, creating a backfire.
Although rare, your ignition module might be causing Ignition Mistiming.
It is the motorcycle components witch tell your spark plug when to fire.
It could be out of sync with the combustion timing.
The fix
Check your spark plugs for signs of wear and tear and replace them if needed.
If it doesn’t work, replace your ignition module if you suspect ignition mistiming.
8. Damaged valves
The intake and exhaust valves control air and fuel into the combustion chamber and then empty it.
One of them might have bent over its work-life or not seal correctly.
As a result, poor combustion occurs.
Fix
Get the engine apart. Get the valves checked and replace them if you need to.
Final Word on Motorcycle Backfirering
I hope this article helped you find what you were looking for and get your bike to stop backfiring.
Or don’t fix it yet. 🙂
Backfires can create a nice sound on many motorcycles but do it in moderation.
Please don’t abuse it. Enjoy it if you do but do take the time to find the problem before it gets worse.
Have fun. Ride safe.
