Why Does My Motorcycle Carburetor Spit Out Gas?

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If you own a motorcycle, you may have been unlucky enough to suddenly start having your bike shoot gas out of the carburetor. Rightly so, you should be concerned about this.

You may be asking, could this damage something? Is it safe to ride like this? If your motorcycle carburetor spits out gas, it can be caused by a bad float needle valve. It could either just be stuck or it could be worn so badly that it no longer works right. By fixing or replacing the float needle valve, you can usually resolve your issue.

This might be a stressful problem but we will try to get you back out on the road as soon as possible. Your bike may be new or old, but there is always a way to fix it. In this article, we will teach you why it is spitting gas and then how to fix it.

Why The Carburetor Is Spitting Out Gas

So why is your motorcycle spitting gas out of the carburetor? As we previously mentioned, there is one main cause that usually leads to this. This cause is a bad float needle valve. The float needle valve has a very important but simple job, as it regulates the flow of fuel. As this float starts to wear, it will prevent the valve from actually closing. This means that you will have a constant flow of gas. This starts to flood the engine, shoot gas out of the carburetor, and can even soak your air filter.

You might notice these problems occur after your bike has sat parked for a very long period of time. Over this time period, the gas that is sitting in the carburetor will go bad. Be sure to avoid using gas with more than 10% ethanol. The ethanol will quickly wear away at your float needle valve and cause it to go bad. Ethanol-free gas is the best to run with if you want your rubbers to last as long as possible.

Lastly, this could be a result of modifications that you have made to the bike itself. If you make major exhaust changes, that can affect the engine quite a bit. While this can have big impacts on things like back pressure, flow, and sound. Generally, the engine isn’t re-tuned, and timing isn’t adjusted to match that. As a result, you may be running too rich and over-fueling the bike. Some tuning on the motorcycle should resolve this issue.

Is It Dangerous?

You may wonder, is it actually bad for your bike if this happens? The answer is yes. The overflowing of the engine can cause engine damage. As the fuel overflows, it will start to flow back into the intake. To do this, it will have to run down the actual cylinder walls. This is bad for many reasons. The first is that it will contaminate your oil and prevent it from being able to properly lubricate everything. Secondly, it will be causing extra wear on your piston rings. Obviously, these are both very big deals as they can result in a need to replace or rebuild your engine. 

Secondly, there is a safety concern with gas spitting out of the carburetor. This gas is still very much flammable. High temperatures can cause the fuel to ignite, leading to a fire. You do not want to be riding your bike while it is spraying fuel all over the place. This could cost you your bike or even your life if it were to catch fire suddenly.

If you notice that your carburetor is spitting out fuel, you will want to fix this as soon as possible. This will help keep you safe and make sure that you are not causing extra damage to your bike. Taking the time to get your bike running correctly before riding it will pay off huge dividends down the road. It can ultimately save you thousands of dollars down the road as a result of major engine damage.

How To Fix A Spitting Carburetor

Your carburetor performs a very important job on your bike. It is responsible for providing the right mixture of gas and air to your engine. It does this by first regulating the flow of air through them. As air flows through the main bore, it sucks fuel into the air stream. This mixture then flows through the intake valve and into the engine.

If your carburetor is spitting out fuel, you will need to get that repaired as soon as you can. Even if you think you know what is causing the fuel to spit out, you should always diagnose the issue first. This can save you a lot of time and money down the road. Taking the time to figure out what exactly has gone bad on your bike should always be your go-to move before replacing things.

If you find that the float needle valve is in fact the issue, you will need to replace or repair it. Depending on your specific make and model, there are repair kits available that will allow you to bring your stuck or worn valve back to life and save you a lot of money. You always can replace the entire unit as well. Depending on your specific make and model, there are also aftermarket “upgrades” available that claim longer life and better performance.

If you find that your issue is a result of tuning, you will need to do a little bit of tuning to bring things back to where they should be. You can adjust the carburetor to have the bike run leaner or richer. If you need to adjust other software-controlled timing, you may need to take your bike to a professional to do so.

If you do experience this issue, it is a fairly common issue that many people don’t know how to resolve. There are tons of different posts on motorcycle forums for almost every different make and model. Take a look on there for your specific bike and you may be able to gain some insight into what may be causing this and how to fix it yourself.

How To Prevent A Motorcycle From Spitting In The Future

So, how can you prevent your motorcycle from spitting gas out of the carburetor in the future? As mentioned previously, the most common cause of this problem is a bad float needle valve. The best way to prevent this phenomenon from occurring is to make the float needle valve last and function properly for as long as possible.

The number one best thing that you can do for your float needle valve is to watch what fuel you are putting into your bike. Ethanol is the worst enemy to your float needle valve. As such, you will want to pay attention to the ethanol content in your fuel. The higher the ethanol content, the quicker the rubbers will get eaten up. This causes the valve to get destroyed. If you get ethanol-free gas, this would be the best thing for the longevity of the plastics. If you use E85 fuel in your bike, your float needle valve will pay the price almost immediately.

The second major thing that you can do to avoid having your carburetor spit out gas is to avoid letting your bike sit idle for very long periods of time. If you do, the gas will become old and therefore dangerous for the carburetor. If you frequently or even occasionally do this, you might notice symptoms like these. Even if you will not be riding your bike much for the next little while, it’s still a good idea to get out and start it every now and then to cycle fuel throughout the engine. This will help your bike run as it should for as long as possible.

This article has been reviewed in accordance with our editorial policy.

Kyle Cannon

Kyle currently works as a mechanical engineer and graduated with a minor in automotive engineering. He loves restoring motorcycles, has a vast knowledge of how they work, and has sold his restoration projects to customers from all over the United States.

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