While you are riding down the road on your motorcycle, you may hear a quick, loud pop and a banging sound coming from the exhaust of your motorcycle. When a motorcycle backfires, it makes an irritating sound and can also be dangerous for the motorcycle itself.
If you’re having trouble with backfiring, you shouldn’t ignore these nine causes. That way, you can easily figure out what’s wrong and fix it.
Why Is My Motorcycle Backfiring?
Motorcycles can backfire for a variety of reasons, including wrong jetting, infrequent spark, exhaust replacement, a dirty carburetor, incorrect timing, too much or too little gasoline, poor fuel quality, an exhaust pipe that is too short, and a leaky exhaust pipe.
1. Incorrect jetting
It’s possible that the bike you purchased was never properly jetted, or that it’s not jetted properly for where you ride. Motorcycle backfire causes dynojet.
The effects of humidity and elevation on bike performance are significant.
So much so that most motorcycle manufacturers will offer models in both the US and the EU, with different jets.
Taking a bike that has been jetted for one level of elevation and humidity and riding it somewhere else will solve the problem.
This is usually the case when purchasing an imported bike.
As previously stated, an ECU override (DynoJet) or having a local motorcycle specialist determine whether the bike is running lean or rich and jet it accordingly will be required.
2. Infrequent spark
An annoying issue is an intermittent spark. It’s difficult to diagnose and pinpoint, but here are some warning signs that this could be your case.
If your motorcycle only backfires at certain times, such as when it’s extremely cold or hot, when it rains, when you turn left, and so on, you may have intermittent spark.
An intermittent spark occurs when the spark plug normally fires the majority of the time but fails to spark on occasion, causing your engine to backfire. When there is fuel and air in a cylinder but the spark plug does not ignite it, the mixture is pushed out during the compression stroke and as soon as it hits the exhaust valve.
The spark plugs, wires, or ignition coil can all cause an intermittent spark. To inspect a spark plug, unscrew it from the cylinder head and place it against the side of the engine. If the spark plug is sparking at regular intervals, move on to the next one and check all of them.
3. Exhaust upgrade
This is most likely the source of your backfire problem if you purchased a used motorcycle with an aftermarket exhaust.
Original equipment exhaust systems are designed to work with standard jetting.
The majority of aftermarket exhausts are designed to improve performance, but they rarely work with stock jetting.
Your bike must be properly jetted to accommodate the new aftermarket exhaust.
There are a variety of electronic components for fuel-injected motorcycles that can override ECU fuel settings (such as DynoJet or the JD jetting kit) to ensure that your bike has the proper air:fuel ratio.
Your local motorcycle specialist will be able to jet your machine properly for standard carbureted motorcycles.
4. Dirty carb
If your motorcycle has a backfire and is carbureted (rather than fuel injected), you should disassemble it.
A small amount of dirt can cause issues.
Remove the carburetor from the bike and empty the float bowl of fuel.
All jets and the carburetor housing should be removed and thoroughly cleaned with carb cleaner.
If you find more than a few specks of dirt in your carb, you’ve got a bigger problem: air flow.
If you ride in dusty or muddy conditions, you should start doing more regular maintenance (for example, motocross, dirt bike, enduro, and adventure riders).
Maintain your air filter by cleaning, lubricating, and sealing it on a regular basis. If you want an entire piece of writing that describes the process of cleaning a carburetor, read how to clean a carburetor on a 4 stroke bike.
5. Incorrect timing
When it comes to troubleshooting motorcycle problems, having the right basic tools on hand is always a good idea so you can do these repairs in the comfort of your own garage. View my list of recommended motorcycle tools by clicking here.
Motorcycle timing systems are classified into two types: electronic timing and points/condenser setups. Most motorcycles built after 1970 have electronic timing, making life much easier.
Electronic timing has simplified troubleshooting because there are fewer parts to rule out as the source of a backfiring problem.
When one of the cylinders is about to fire and is in its compression stroke, electronic timing sends a voltage signal to the ignition coil.
When the ignition coil receives this voltage signal, it dumps its stored voltage, which travels through your spark plug wire, spark plug, and eventually ends up as a big spark right at the top of your cylinder.
6. Too much or Too Little fuel
For the combustion process to be successful, there must be a certain amount of air and fuel inside the cylinder. If either is present in excess, the combustion will be weak and may damage your engine.
The phrase “my motorcycle is running rich” indicates that the cylinder is receiving too much fuel and not enough air. ‘
A rich condition on an engine is dangerous and should be avoided. Running rich reduces your miles per gallon and can cause severe backfires in your exhaust pipe.
If there is too much fuel present in the cylinder then not all of the fuel will be successfully burned during the combustion process.
This unburned fuel will come in contact with atmospheric air and be surrounded by the extremely hot exhaust header.
In the presence of fresh air and high temperatures, the fuel combusts and creates a loud pop or bang sound.
7. Too short of exhaust
Short exhaust pipes can be problematic, and most states have laws governing how long your pipes must be to prevent popping and banging.
Short pipes, also known as shorties, are typically 12 inches or less in length and are designed to give a motorcycle a cleaner look while also increasing exhaust volume.
This is far too brief and will frequently backfire.
Short exhaust pipes are desirable because they give a motorcycle a simple and small design, but never go shorter than 12 inches due to the negative effects.
Pipes that are extremely short typically lack an integrated baffle. A baffle is a small section of pipe that functions similarly to a car muffler.
It attempts to convert the turbulent exhaust flow into a more laminar, quiet flow.
I always recommend getting an exhaust pipe with a removable baffle so that you can remove it if your state allows louder exhaust, but if you’re going on a road trip, you can simply slide the baffle back in and you won’t be pulled over.
Shorter exhausts also tend to backfire more because there isn’t as much pipe length to smooth out turbulent air as the motorcycle was designed for.
Motorcycle exhaust pipes are made to be a certain length so that they use the least amount of gas possible.
Shorter pipes sacrifice efficiency for higher performance, but that performance comes at the expense of a higher risk of backfire.
8. Loose exhaust pipe
To be clear, an exhaust header on a motorcycle is the metal pipe that connects directly to the engine, whereas an exhaust pipe is the last foot or two of pipe that can be disconnected or unbolted.
When I say “loose header,” I’m referring to the section directly next to the engine where hot fumes are pushed out of the exhaust valve immediately after combustion.
I discovered damaged threads on the backside of the cylinder head while working on a BMW R80 for a friend. We were having difficulty tightening the exhaust nut onto the cylinder head, so we decided to leave it alone.
There was a lot of popping coming from that side of the engine when we started the motorcycle. Exhaust was leaking from the crack in the exhaust nut.
Because the exhaust gases exiting the engine have a much higher pressure than the surrounding air, even a small gap between the cylinder head and the exhaust header will allow fumes to escape and cause quite a commotion.
The best solution is to tighten your exhaust headers. Some people use nuts, others bolts, and still others compression fittings.
If a bolt has broken off, seek repair assistance from a welder or machine shop; however, I would not recommend riding much with that problem because it will only worsen.
Some motorcycles vibrate so much while running that the exhaust nuts eventually loosen.
Check the exhaust header connection every few months as part of your preventative maintenance.
9. Poor fuel grade
Backfires caused by insufficient fuel are less common than the other problems, but I have seen them. This occurs occasionally when people replace their stock intake air box with inexpensive pod filters (which is what I did).
See my guide on air boxes vs. pod filters for more information.
When you run lean, you have too much air in your cylinder and not enough fuel. A lean state in your engine is extremely damaging to its internals.
Your backfiring issue could be caused by a lack of fuel in the cylinder and an excess of air. The massive amount of air present can suppress combustion when the spark plug attempts to ignite the air-fuel mixture.
If you’ve used ethanol-additional gasoline, you’re bound to have carburetor problems sooner or later. I made a video series about restoring motorcycles that includes a detailed 25-minute video on how to clean and rebuild carburetors.
Why Does My Motorcycle Backfire On Deceleration?
If your motorcycle backfires on deceleration, it’s usually because of a problem with the engine timing. When you decelerate, the engine RPMs drop and the mixture of air and fuel in the cylinders becomes too lean.
One way to fix this is to adjust the carburetor so that it’s delivering more fuel when you’re at lower speeds. Another way to fix it is to install a set of aftermarket pipes that have a different backpressure profile than the stock pipes.
If your motorcycle has been backfiring on deceleration for a while, it’s also possible that the valves are out of adjustment. This is something that should be checked by a qualified mechanic.
Why Does My Motorcycle Backfire At Idle?
One of the most common reasons your motorcycle backfires at idle is because the engine’s idle circuit is Adjusting the mixture screws will usually fix the problem.
Another possibility is that your motorcycle’s engine is running too lean. This can be caused by a number of things, including a dirty air filter, a clogged fuel injector, or a leak in the intake manifold.
If you’re not sure what’s causing your motorcycle to backfire, take it to a mechanic for a tune-up. They’ll be able to diagnose the problem and get your bike running smoothly again.
What Causes A Motorcycle To Backfire When Starting?
There are actually a few different things that can cause your motorcycle to backfire when starting it up.
One possibility is that the carburetor is flooding.
This can happen if you’ve been riding your motorcycle and then turn it off for a while without letting it cool down first.
When you go to start it up again, the fuel in the carburetor has had a chance to evaporate, which can cause the engine to flood.
Another possibility is that the spark plugs are fouled. This can happen if you’ve been riding in wet or humid conditions, or if you haven’t been changing your spark plugs regularly.
Finally, it’s also possible that the ignition timing is off. This is something that you’ll need to take to a mechanic to get fixed, as it’s not something that most people know how to do themselves
If your motorcycle backfires, it could be due to any number of reasons. However, there are a few common causes, such as a lean fuel mixture, a clogged air filter, or an ignition timing issue.
There are also a few things you can do to fix the problem, such as adjusting the carburetor, cleaning the air filter, or changing the spark plugs.
If you’re not sure what’s causing the backfire, take it to a mechanic or dealership for diagnosis and repairs.