Motorcycle Backfires When Starting: Reasons & Solutions

Motorcycle Backfires When Starting

Is your motorcycle backfiring while you start the motorcycle? It must be scary to hear those loud exhaustion sounds almost as if the exhaustion pipe was about to burst. And actually, backfiring can be very dangerous if the issue is not fixed as soon as possible. As the backfiring denotes an internal issue of the motorcycle, identifying and fixing the problem is necessary. 

But how would you know what causes the motorcycle to backfire when starting? To identify the issue, you first need to know the possible reasons. And then, you can get an idea about how to fix these issues. For intricate issues, you may need a mechanic. But some issues can be solved easily. 

With all the reasons and solutions for motorcycle backfiring, I am here with this article. After experiencing motorcycle backfires when starting and solving these issues, I am here to solve your query. So stay with me.

7 Reasons Why Motorcycle Backfires When Starting: Know The Cause

Before fixing the issue of motorcycle backfires, you have to identify the problem first. Having an idea about the possible issues can help you find out and solve the issue easily. At least you can check the motorcycle and know which one is causing the motorcycle to backfire. 

Before mentioning the specific issues, know that a motorcycle generally backfires when the fuel combustion doesn’t take place properly. And there are several reasons behind this. So let’s have a look into the reasons why a motorcycle backfires when starting:

1. Excess Fuel:

When there is extra fuel in the tank, there will be fuel that remains uncombusted. There requires a certain mixing of air and fuel for combustion to happen. Now when fuel occupies the tank, air can’t mix with the fuel resulting in poor combustion. This condition is called ‘a rich condition’.

Now how does this cause motorcycle backfiring? As the combustion takes place in a ‘rich condition’, the extra fuel gets released from the tank and moves to the exhaust pipe. Here, the fuel combusts as there is air and the temperature is high. This is when the pipe backfires and roars. 

This not only causes backfiring but also decreases the efficiency of the engine. Your motorcycle will also eat up more fuel than usual and this reduces the longevity of the motorcycle. 

2. Lack of Fuel:

Just the opposite condition of a rich condition can also cause the motorcycle to backfire. This is called the ‘lean condition’ when there is a lack of fuel in the tank. This is another common reason for backfiring. 

When there is scarce fuel in the tank, the air is abundant. But this won’t help as there is not enough fuel for combustion. In this condition, the backfiring is worse than the backfiring during a rich condition. Now when you start the motorcycle, the fuel, and air travel through the hot exhaust pipe, and therefore, the fuel burns resulting in a roar that is backfiring. 

Lack of fuel is very harmful to your engine. And in most cases, the culprit for this is the carburetor. A nasty carburetor restricts the flow of fuel resulting in a lean condition. 

3. Faulty Spark Plug: 

When the spark plug misses out to spark once, the backfiring can happen. In most cases, the fault is in the spark plug. But sometimes, it can also occur due to a faulty ignition coil or faulty wiring. Now when that happens, it is generally a bit difficult to detect. 

What happens when the spark plug doesn’t spark is the fuel and air travel out to the exhaust pipes. There, the fuel combusts which results in a backfire. Now, in this case, you should check the condition of the spark plug. First, detach the plug and earth it by placing the lower side of the engine. Now start the plug and if you see that sparks are being missed, it is faulty. You would need to replace it. 

If the issue is in the coil or wiring, replace them immediately. As a faulty spark plug can cause fatal accidents, you better fix it as fast as possible. 

4. Small Exhaust Tubes: 

Many people install short exhaust tubes to beautify the motorcycle. This also sometimes improves the performance. But in the long term, this is very risky and can be a big reason for motorcycle backfires. 

Small exhaust pipes can’t control the flow of fumes and the surge of the exhaust can make popping noises. Generally, long exhaust pipes slowly release fumes as it travels through the pipe. But as the traveling time through the pipe is less due to the small pipe size, it makes noise. In this way, the fuel is also used effectively and properly. 

So try not to get short pipes and rely on the in-built exhaust pipes of the motorcycle as it is designed to handle the flow of exhaust. Otherwise, you can also use changeable baffles to handle the flow of exhaust. 

5. Wrong Timing: 

The theory of timing is that a voltage is carried to the spark plug which is why it sparks. The signal should be sent at the right time for the spark plug to spark at the right moment. So when you see an issue in the sparking, this can also happen due to wrong timing. 

Most motorcycles use electrical timing nowadays. And the chances of damage are very minimal. But the incorrect timing can happen sometimes. This can happen due to a slightly displaced timing chain, or a faulty exhaust valve can be the reason too. Check both the parts to be sure and then do the needful. In case of wrong timing by electrical timing, it won’t be difficult to solve it. 

However, for a condenser timing setup, the fixation would need a mechanic. But this system is most likely to be in the old motorcycles only.

6. Faulty Exhaust Header:

The exhaust header is the transition between the engine and the exhaust valve. This is a metal tube that connects the engine and the exhaust valve so that the fumes can go out directly towards the exhaust pipe. Now when this transition pipe has a leak or is loose, the fumes can leak too making a nasty popping noise. 

If you hear the noise coming from near the engine, that is probably because of a faulty exhaust header. When the header is faulty, the exhaust gas moves out of the header at high pressure. Due to this air pressure, it makes an extreme popping sound. And this condition is common as the air pressure is very high which can loosen the header. 

In such a condition, you need to tighten or replace the exhaust header. Do check its condition once every 3 months. 

7. Blocked Carburetor: 

When the carburetor is blocked, the air can’t pass properly. The main issue here is when the carburetor is not clean and grease buildups cover the inside of it. When this happens, the engine eats up more fuel than it consumes. This is why there occurs a lack of fuel for combustion. 

As fuel can’t combust in the right place, the fuel is pushed out of the exhaust pipe. As a result, combustion occurs in the exhaust pipe. This is when you hear the loud popping sound. The lean condition occurs mainly due to a blocked carburetor and this is why the motorcycle backfires. 

To prevent this condition, you have to keep the carburetor clean. Ready-made carburetor cleaners are available and you can use them to unblock the channels. 

3 Tips To Prevent Motorcycle Backfire When Starting: 

I have discussed seven possible reasons behind motorcycle backfiring. But what are the solutions to solve these issues? After examining these common reasons, I have found some effective solutions. If you maintain the condition of the motorcycle, you won’t face motorcycle backfires. 

Here are some tips to prevent motorcycle backfire when starting: 

Tip 1- Keep The Carburetor Clean: 

To prevent the lean condition of fuel, you have to keep the carburetor clean. The efficiency of the engine and fuel combustion decreases dramatically when the carburetor is dirty. So make sure to clean it after every 3-5 months. For cleaning, remove the carburetor and dip it in hot water mixed with detergent. With a soft brush, scrub the interior and remove the greasy layers. 

Tip 2- Use High-Quality Fuel:

Using a low-quality fuel that is incompatible with your motorcycle can reduce the efficiency of the engine and build up dirt in the engine and carburetor. The dirt can settle in different areas blocking the free air passage. Therefore, you must use high-quality fuel that suits your motorcycle to prevent buildups. This would keep the passage clean preventing backfiring. 

Tip 3- Check The Condition:

My last tip is to do servicing of your motorcycle from time to time. When you keep checking the condition and take care of the motorcycle parts, you don’t even get the risk of backfire. Check the exhaust valve, header, carburetor, spark plug, and other parts every 3 months so that you can fix the errors. This way you can prevent backfires. 

Frequently Asked Questions:

Is Motorcycle Backfire When Starting Bad? 

Motorcycles backfire when the fuel combustion is poor. The uncombusted fuel causes a fault in timing and spark. This, as a result, reduces the efficiency of the engine as fuel combustion is faulty. As fuel is not used properly, the engine eats up more fuel and the mileage, as well as the power, are affected. So in one word, motorcycle backfires are bad for your motorcycle.

Does Motorcycle Backfire Affect Fuel Mileage?

Though motorcycle backfire doesn’t directly affect fuel mileage, it does reduce efficiency. Motorcycle backfiring causes a loss of fuel as the engine eats up more fuel than needed. This mainly happens when the internal parts remain dirty. As a result, the fuel mileage is reduced as fuel consumption increases. Thus yes, motorcycle backfire does affect fuel mileage. 

What Causes Motorcycle Backfire When Starting? 

Motorcycle backfires due to various reasons. When there is extra fuel in the engine, the excess fuel combusts in the exhaust pipe causing a backfire. This can also happen when there is inadequate fuel and the carburetor is dirty. From this issue, a lot of other issues appear causing motorcycle backfiring. 

What Causes Backfire On Startup?

There are different reasons for backfire on startup. Some common reasons are:

  • Faulty spark plug,
  • Dirty carburetor,
  • Insufficient fuel,
  • Excess fuel,
  • Low-quality fuel,
  • Mistakes in timing,
  • The short exhaust pipe,
  • Faulty exhaust valve.

These are the common reasons why motorcycles backfire on startups.

Does Backfire Hurt the Engine?

Backfiring doesn’t directly hurt the engine. But gradually, backfire reduces the power and efficiency of the engine. As fuel is not combusted timely and the fuel consumption is faulty, the engine can’t use the fuel properly. As a result, the mileage is reduced and the engine power decreases over time.

Does Bad Gas Cause Backfiring?

When the air and fuel mixture ratio is not appropriate, this can cause backfiring. This condition occurs during rich and lean conditions. These are the conditions when the fuel and air ratio is not exact. This results in bad gas and as a consequence, the motorcycle backfires. Therefore, it is important to keep the air-fuel ratio correct to prevent bad gas production. 

Can A Bad Spark Plug Cause Backfire? 

A bad spark plug can cause a backfire. When the spark plug is faulty and there is a mistiming of sparking, there can happen a motorcycle backfire. A faulty spark causes fuel and air to combust in the exhaust pipe. As a result, the combustion causes backfiring out of the pipe.

How Do You Fix A Motorcycle Backfire? 

To fix a motorcycle backfire, you have to keep the passage clear of passing fumes. Therefore, you have to keep the carburetor and exhaust passages clean so that the fumes can go out freely. Also, to maximize the efficiency of the engine and use the fuel, you have to keep the parts clean. Besides, you have to use high-grade fuel and put an ample amount to maximize the efficiency. 


Now you know the reasons behind the motorcycle backfire when starting. The problem can cause serious consequences but these issues are controllable. If you look into the tips, you can find the solutions. 

I hope now you won’t face motorcycle backfires. 

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