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Why Is My Dirt Bike Backfiring? Simple Causes & Fixes

Is your dirt bike backfiring and you’re wondering if it’s safe? Whether you’re new to dirt biking or just want to quickly fix your bike, you’re in the right place!

In this article, I’m going to show you what backfiring is on a dirt bike, why you may or may not need to get it fixed right away, and how to troubleshoot it based on the specific symptoms you’re having.

What is a backfire on a dirt bike?

A backfire is simply an explosion of excess gas, usually in the exhaust, but can also happen in the intake. It’s caused by a number of things, such as a lean jetting mixture or a flooded engine. 

2 stroke and 4 stroke dirt bikes can both cause backfiring, but it’s much more common to hear and see it on a 4 stroke engine. 

This is because a 4 stroke typically has higher exhaust gas temperatures, which make it more likely to ignite and combust the gas into an explosion (backfire). 

A muffler exploded possibly from the dirt bike backfiring and getting too hot
Muffler explosion caused by backfire?

Can a backfire damage your dirt bike?

Depending on how bad your backfiring symptoms are, yes, it can damage your dirt bike. Whether it’s a jetting issue that can cause excessive wear on your engine, or a big enough backfire that creates enough pressure to damage the intake or exhaust.

Why does your dirt bike backfire?

There’s a variety of reasons why your dirt bike may be backfiring, but we need to figure out when it’s doing it to better diagnose and fix the real problem. 

Backfire after changing exhaust system on a dirt bike

If your dirt bike ran well before but when you modified or upgraded the exhaust, it’s common to have it backfire as a result. Whether it has a carburetor or a fuel injection system, there’s only one way to fix it.

When you swap exhaust systems, the exhaust flows differently – generally more if it’s an aftermarket pipe or muffler. This can cause it to run leaner, which results in backfiring and running hotter.

A fuel injection system will NOT compensate for a different exhaust because it doesn’t measure the exhaust gas temps. So, you need to tune the jetting/fuel mixture to get it to start and run well again.

Backfires But Won’t Start

If your dirt bike backfires when starting but won’t start, it could be caused by a couple different issues. Poor jetting for your climate is a likely cause. 

However, if you’re just trying to start it after engine rebuild, then there’s a chance that something is not installed correctly. This could be a camshaft that’s not properly timed, so the valves are opening at the wrong time. 

Poor jetting causing backfire – lean or rich?

Diagnosing a backfire can be tricky if you’re new to troubleshooting because it could be a lean or rich jetting mixture. Let’s look at each symptom to help determine which way you need to go.

A backfire when trying to start often means that there’s too much gas in the engine and/or carb. This means that the engine is trying to ignite it but there’s too much and it just “pops” some of it away. 

A rich jetting mixture is a common issue when this happens, whether it be too big of a pilot jet or a clogged air filter. Try leaning out the air screw or fuel screw and see if it helps. 

Another common problem is from trying to kick start your dirt bike too many times. If you have a poor starting technique or the carb is a little dirty, 

Backfiring On Deceleration

Whether it’s a “pop”, “bang”, or “crackle”, backfiring when slowing down is fairly common on a 4 stroke dirt bike, but is it safe?

A little bit of popping on deceleration with the throttle closed is okay, but a lot of banging and popping will eventually do some damage. In either case, backfiring when slowing down on a dirt bike is usually caused by lean jetting.

When you close the throttle, the engine is still sucking air and fuel through, but if the pilot jet is too small, not enough fuel will be sucked into the engine. This is why a lean pilot jet circuit causes deceleration backfire.

Backfiring On Acceleration

Trying to twist the throttle but it backfires out the exhaust pipe? This is often the result of a very rich fuel mixture.

It can cause pretty big flames to shoot out the muffler, which is why USFS-approved spark arrestors are required for trail riding on public trails. If you’re consistently seeing flames, you need to get it fixed.

A rich fuel mixture could be from a jet circuit that’s too rich, but it could also be caused by a weak spark, incorrect engine timing, or a clogged air filter/intake. You need a proper mixture of air and fuel for your dirt bike to start, idle, and run well.

If you ride at different elevations, then I highly recommend you learn how to tune your jetting, whether it’s a 2 stroke carb or a 4 stroke carb. The temp, elevation, and humidity all play a role in how your bike runs.

Backfire Through Carb

A backfire through your dirt bike carb is typically caused by a lean mixture. When the engine is starving for fuel, it can ignite the fuel in the carb, resulting in a backfire through the intake.

First, make sure that your carb is getting enough gas to the carb – especially if you just had the tank or carb off. It’s easy to pinch or reroute a fuel line that causes problems.

It’s also possible that you have an air leak in the intake system, feeding the engine too much air. Make sure all the carburetor clamps are properly tightened and there’s no cracks in the air boot or intake manifold. 

A quick spray of carb cleaner or something flammable around the carb will tell you if there’s an air leak – the engine RPM will change when you spray if there’s an air leak.

Causes of backfiring on a dirt bike

These are the most common reasons why your dirt bike is backfiring:

  • Rich jetting
  • Lean jetting
  • Air leak
  • Incorrect cam timing
  • Weak or loose spark plug
  • Clogged air filter
  • Worn valves

3 easy steps to prevent engine problems

Many dirt bike riders make the same mistakes that cause catastrophic engine failures. I want to show you the 3 simple steps to prevent major engine problems so that you don’t blow up your bike or get stranded in the middle of nowhere – tap here to learn more.