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What Is Motorcycle Backfire? [Causes & Best Fixes]

Motorcycle backfire is something that happens when a motorcycle engine gets too much fuel or air. Bikes comes setup so that the carburetor (or fuel injection system on modern bikes) provides the correct ratio of fuel and air, to allow the bike to run at its best.

Extra power can be extracted via various mods (including exhausts), but the bike needs to be jetted to suit. If your bike isn’t jetted correctly, it’s worth getting it setup by a mechanic (for carbed bikes), or, for fuel injected bikes, get an ECU flash, or use something like the DynoJet. A cheaper option (if you’re ready to jet your bike manually), is something like the JD jetting kit; I’ve used this on MX bikes in the past.

Before spending chunks of money (for pre fuel injection/bikes with a carb), I’d always recommending cleaning your carb using the appropriate fluid (usually under $15 and will last 5+ cleans).

Motorcycle backfire can happen on:

  • Start up
  • Deacceleration
  • Acceleration

When it happens, you’ll hear sounds such as:

  • Popping
  • Banging

Why do motorcycles backfire?

All combustion on a motorcycle should happen in the combustion chamber. A backfire is a combustion that’s happening outside of the combustion chamber.

Put simply – your bike is burning fuel (and exploding) where it shouldn’t be.

If you’ve got some freaky looking flames coming out of your exhaust, combustion is happening there, rather than the combustion chamber.

But why?

Running too rich

The engine is being starved of air and is being swamped with fuel.

Running too lean

The engine is being starved of fuel and swamped with air.

What are the most common causes of motorcycle backfire?

So, what can cause a motorcycle to backfire?

  1. Exhaust upgrade
  2. Incorrect jetting
  3. Poor fuel grade
  4. Dirty carb

1. Exhaust upgrade

If you’ve purchased a second-hand motorcycle that has an aftermarket exhaust fitted, this is the most probable cause of your backfire problem.

OEM exhausts are designed to work with standard jetting.

Most aftermarket exhausts are designed to extract additional performance, but they rarely work with standard jetting.

The fix

Your bike needs to be jetted correctly to suit the new aftermarket exhaust.

For fuel injected bikes, there are various electronic components that can override ECU fuel settings (such as DynoJet or the JD jetting kit) to make sure your bike gets the right air:fuel ratio.

For standard carb fuelled motorcycles, your local motorcycle specialist will be able to correctly jet your machine.

2. Incorrect jetting

It may be the bike you’ve purchased was never jetted properly, or it’s not jetted correctly for where you ride. motorcycle backfire causes dynojet

Humidity and elevation affect a bike’s performance dramatically.

So much so that most motorcycle manufacturers will have US and EU model, and these bikes will be jetted differently.

If you’ve taken a bike that’s jetted for one level of elevation and humidity and ride it elsewhere, correctly jetting it will solve the issue.

Typically, this is the case if you purchase an imported bike.

The fix

As above, you’ll need to either get an ECU override (DynoJet) or have a local motorcycle specialist determine if the bike is running lean or rich, and jet it to suit.

3. Poor fuel grade

The higher the performance of your motorcycle, typically the higher-grade fuel it will use.

That’s because a higher performance engine is less reliable, and even the slightest internal change will affect output dramatically.

Essentially, something like a tourer is going to be a lot less sensitive to change than a track bike.

The fix

If you’re using standard grade fuel from gas stations, opt for the higher-octane fuel.

Even filling up every-now-and-then using higher octane fuel will help to clean out the fuel system.

4. Dirty carb

If you have motorcycle backfire and your bike runs a carb (rather than fuel injection), it’s time to rip it apart.

Even the smallest piece of dirt could be causing issues.

The fix

You’ll need to remove the carb from the bike and drop the fuel from the float bowl.

All jets should be removed and cleaned using carb cleaner, as should the housing of the carburetor.

If you find more than a few specs of dirt in your carb, there’s a bigger problem at hand; air flow.

If you ride in dusty or muddy conditions (for example: motocross, dirt bike, enduro and adventure riders), you need to start doing more regular maintenance.

Make sure you clean your air filter regularly, lube it, and seal it to the airbox housing with a thin layer of grease.

Is backfiring bad for motorcycles?

Simple answer? Yes. A backfire is a fuel malfunction. Any combustion outside of the combustion chamber is going to result in a loss in power.

Ironically, a lot of riders buy expensive exhausts for extra power and purposely make them backfire.

More crucially, running a bike too rich or, too lean, can result in the internal temperatures of the combustion temperatures getting too hot.

Long story short, you’re frying your engine! And that means it’s not going to last as long as it should, or provide the performance that it’s capable of.

What’s next?

Hopefully that’s uncovered a few reasons your motorcycle is popping, and what you can do about it.

And now your bikes ready to rock, check out our guide to the best motorcycle stands.

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