Motorcycle Backfire Causes [And The Best Fixes]

David Welch
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What Is Motorcycle Backfire?

Motorcycle backfire is a loud noise created by the exhaust system on a motorcycle. It is not something that you should be worried about, as it normally occurs when the engine is started. If the problem becomes persistent, however, you could potentially need to visit your mechanic.

The backfiring noise happens because the motorcycle’s engine cannot keep up with the amount of fuel injected into the cylinder. The air and fuel mixture ignites as it should, but rather than a controlled burn, it is a sudden ignition. This sudden ignition causes the backfire noise.

Some motorcycles are prone to more backfiring than others. It is more common in older motorcycles. If the backfiring sound becomes chronic, you may need to have a look at the ignition sensor. The ignition sensor is located on the top of the spark plug. It converts the signal from the ignition coil into a signal that is passed to the spark plug.

Why Motorcycles Backfire

When a carburetor cannot supply adequate amounts of fuel to an engine when it needs it, a motorcyclist may experience backfiring. The engine may hesitate on acceleration or may backfire when exiting a driveway or when traveling at lower speeds. Backfiring is often due to a carburetor that is out of adjustment or because fuel flow is not being properly regulated by the throttle cable. When it occurs, backfiring is not usually indicative of engine failure.

Running Too Rich

One of the most common causes of backfiring in motorcycles is too much fuel. The engine will be receiving too much fuel if the pilot jet size is larger than the pilot jet size the manufacturer recommends. You will have to go down one size on the pilot jet.

Running Too Lean

Running your bike too lean will cause backfires. This is because the spark plugs and your engine are looking for air and fuel in a ratio of 14 to 1.

For every 14 volumes of air, there needs to be 1 volume of fuel. If there’s too much air and not enough fuel, the engine will run lean.

Bikes that run lean will also cycle easily, sometimes even when the throttle is closed. This happens because the engine can’t compress the air. That extra air raises the temperature of the plugs.

What’s more, a lean engine wastes fuel. That’s not just because it’s making less. It’s also because it’s wasting the effort that it’s using to expand the air.

The result is that you’re using more fuel than you need. To fix this, you’ll need to add fuel to the mix. To find the proper ratio, keep track of how much you’re riding and what RPM your bike is maxing out at. For every 10 miles, your engine should have a range of 4000 RPM. Use this to get a sense of what your engine looks like when it’s perfectly balanced.

The Most Common Causes [And Fixes] Of Motorcycle Backfire

Motorcycle backfire is one of the most common riding problems. Riders often fear that motorcycle backfiring is an indication of something much more troubling. Although backfire in motorcycles is often normal, when it happens unexpectedly it is always cause for concern.

Common Causes

One of the most common reasons for motorcycle backfire is gas peddling. When the gas peddle is held down too long, pressure builds up in the carburetor. This pressure causes fuel to be forced out into the exhaust. The momentum of the exhaust will make the fuel go out faster than the bike is moving, causing a backfire.

Another cause of backfire is a clogged air filter. If the air filter becomes completely clogged, the excess pressure will be forced out through the exhaust port. Before each ride, open the filter and clean the inside of the filter from the previous trips elements.

A more serious issue is bad spark plugs. Over time, the parts of the spark plug can become worn. This can cause an improper spark, which can cause backfire. To solve the problem check the gap of the plug. If it is too wide, it will not work to ignite the fuel. Not wide enough will cause the plug to break and create a backfire.

Exhaust Upgrade

Backfiring is something that happens rarely, but if you’re experiencing this problem while riding your motorcycle, it can be unnerving.

The best and easiest way to fix this problem is to upgrade your exhaust system. This is a very inexpensive fix.

Lower End Models : The exhaust pipe on a cheaper model of motorcycle may be too cheap to allow the gases to escape easily. The pipes may also not be engineered to allow enough space between the exhaust pipe and the engine block.

Higher End Models : Higher end models have a larger exhaust system, and this is what causes backfiring.

If you’re experiencing this problem, move your exhaust pipe as far away from the engine as possible. You can also add heat shielding so that the exhaust pipe isn’t directly near the engine block. If you don’t want to deal with it, you can always replace your exhaust system.

Incorrect Jetting

Backfiring is not a concern when the bike is in idle and there are no other noises generated. Although it is normal for the fuel to combust during the ignition process, this is not the same as backfiring. Normally, this problem will present itself in the situations in which the issuing from the exhaust equals in intensity as the fuel combusting. The exhaust of the bike when backfires will be as loud, if not stronger, than the distinct sound of the spark plug igniting the fuel.

This is caused by the incorrect jetting of the bike. This prevents the engine from running at the proper speed. In turn, this means that there is a lack of airflow into the engine, which in turn causes the engine to fire in the incorrect manner.

The best fix for this is to rejet the carburetor. The process is simple enough. You will need to remove the carburetor, and manually pull off the slide that is attached to the main jet of the carburetor. Then remove the jet and replace it with another one. This one that you will need to replace will equal the one that the bike was supposed to come with.

Even if you have an exhaust system on the bike, this should not be a problem for you. At no time will you need to remove the headers from the motorcycle.

Poor Fuel Grade

Poor fuel quality can be the cause of noisy backfiring. If your gas has a low enough octane rating, backfiring is one of the symptoms of using it. Low octane causes a lot of issues and should be a big concern for those who are concerned with improving their bike’s performance. This is because low octane will cause knocking, which is the most effective way of decreasing the efficiency of your engine.

Fuel which has water in it will also cause backfiring. This is especially true if the gas contains ethanol, which sinks to the bottom of tanks and causes poor compression. Fortunately, this is easy to fix. All you need to do is remove the jets from the carburetor and clean them. After that’s done, put the jets back in and adjust the compression as well as the choke setting to see if there’s still backfiring. If that’s not the culprit, then there may be something wrong with the jets themselves, which you can take care of by doing a few simple things:

First, you’ll need to clean all of the jets by soaking them in alcohol.

You can clean them by taking them apart and using a brush to clean the individual parts and jets.

Dirty Carb

There are many things that can cause your motorcycle to backfire. You should make sure that before you try to diagnose the problem, you have ruled out the easy ones. After all, if you hear a motorcycle backfiring, it’s likely you have a problem somewhere.

Most problems have you spending a little bit of money, but if you end up getting a big repair bill, you can start by cleaning the air filter and the carburetor. This is actually easy to do, and for a dirt bike or a motorcycle, you can do it yourself. Actually, pulling the air filter off is almost enough to tell you if that’s the problem. If it’s filthy, clean it up.

If you still have a problem, you might have a vacuum leak. These can be caused by bent hoses or loose clamps. Fix those or replace them. (It’s worth noting here that you can go to your local mechanic and have them look it over properly. Depending on your distance, that may not be a bad idea.)

As you’re checking the hoses, check the filter you just cleaned. If it’s cracked or damaged, get rid of it and get a new one.

Is Backfiring Bad For Motorcycles?

Most people have experienced backfiring their motorcycle at some point. It’s most often during a cold motorcycle start and it can cause the rear wheel to jerk and stutter.

Backfiring is caused because a cylinder isn’t firing properly. Do not confuse this problem with what’s called “dieseling,” or loud “banging” that is often mistaken for backfiring.

It can happen in any type of engine, car or motorcycle.

If you experience a sudden backfiring or feel a jerk in your rear wheel, you can check the following items:

  • Check your charging system. If it’s not at full charge, it will cause backfiring. This is because the cylinders won’t have the fuel they need to build enough pressure for a smooth run.
  • Check your ignition timing. This problem doesn’t always mean that your timing is off, but it’s worth checking to make sure. Backfiring often occurs at idle because it’s when the ignition timing is at its most sensitive. Even if the timing is a bit too advanced or retarded, the engine may run louder and run smoother.

What’s Next?

When you’ve completed a purchase you head out to the parking lot to test out the motorcycle. It’s exhilarating, timeless, and a bit of a rush.

But, then it happens; a backfire; an unexpected explosion of gas in the exhaust pipe. What does this mean? What causes this and what can be done to avoid a backfire?

What Causes A Motorcycle To Backfire?

The two main causes of backfire in motorcycles is either a clogged or damaged exhaust pipe or a fuel leak caused by a bad gas cap. These issues are easy enough to diagnose if you know what to look for.

Symptoms that Point towards a Bad Exhaust Pipe

Carburetors and poor fuel injectors can sometimes contribute to backfiring on their own. But, backfire caused by a damaged exhaust pipe is likely the common culprit when it comes to the occasional backfire.

Some significant symptoms that can point to a consumed exhaust pipe are louder than usual knocking sounds and slight knocking that increases in frequency as more gas is added to the tank.

Often the exhaust pipe will have a black line of soot visible due to worn on its surface. Exhaust pipes can even melt if worn too much; causing the final blow and a sudden sharp loud backfire that stops the motorcycle.