7 Reasons Why Your Motorcycle Exhaust Smells Like Gas


Owning a motorcycle is not anything like owning a four-wheeled vehicle. One benefit to riding a motorcycle is their issues can usually be taken care of on your own. You should be able to fix any issue that comes without the need to take your motorcycle to a mechanic.

There are many issues that you will need to check if you are smelling gas coming from the exhaust of your motorcycle. Read on to learn the top reason your motorcycle’s exhaust may start to smell like gasoline. It is important to get any issues that may be going on under control before they create a bigger issue.

Leaking Fuel Lines

Black Yamaha motorcycle next to a gas pump in Canada
Photo by Andrew Pham on Unsplash

A motorcycle can start to smell like gas is coming from various parts of the bike if there are leaking fuel lines. Fuel lines need to be checked along with regular maintenance to double-check that they are not coming loose or dripping fuel.

If you smell fuel coming from any part of your bike this is typically the first place you will want to check. It is a quite common issue for lines to loosen over time as the bike bumps and vibrates down the road. Double-check that the fuel lines are intact and there is no fluid on them.

Leaking Fuel Tank

Motorcycle white fuel tank shot from above
Photo by Maarten van den Heuvel on Unsplash

If you are smelling fuel, you may want to look at your gas tank. It is where the fuel is stored on your motorcycle, these places are:

  • Fuel valve
  • The tank itself
  • Where the lines meet the tank

In some cases, leaks can be clipped and tightened with fastening clips. If these parts are dry and do not smell of gas, then the leak is not coming from them. You will need to look a little more in-depth to see what could be causing your exhaust to smell gas.

Your Fuel Ratio Is Off-Running Rich

Close-up of a Yamaha motorcycle engine
Photo by David Lundgren on Unsplash

When your bike has too much gas in the fuel tank this will not allow air to move through the combustion chamber of the engine. There are a few ways to check to see if this is the issue which are:

  • Check if your spark plugs have black tips
  • Checking the float needle
  • Fuel smell not coming from the fuel lines themselves

If your issue is your motorcycle running rich with too much fuel, you will need to typically clean your carburetor and replace your spark plugs. Keep in mind that you should not fill your fuel tank full as this will only cause you to run rich.

Flooding a Carburetor

Black & white shot of a person holding a motorcycle carburetor
Image by Joseph Emmanuel Japos from Pixabay

A carburetor can have several things go wrong with it. If you are having issues with your bike one of the first things, you can look at (after fuel lines) is your carburetor. The carburetor can become flooded which will create strong sent of fuel coming from your bike.

This can happen if you have clogs in your air filter or issues with the carburetor in general. A bad carburetor can cause your bike to ride very rough and misfire which is not good long-term. If you think your carburetor is the issue it may need to be replaced.

Bad Mass Flow Sensor

Close-up of a BMW motorcycle engine
Image by 2427999 from Pixabay

The flow sensor is telling the amount of air entering the fuel injection. There are a few reasons to tell if your motorcycle has a bad mass flow sensor which are:

  • The engine is hard to turn over
  • Motorcycle stalls quickly after starting
  • Jerking while accelerating

If these issues are happening, you will need to get your bike to a mechanic to thoroughly diagnose the issue. The airflow sensor should be cleaned regularly and every time you change the oil in your bike.

Gas Vapors Form on a Hot Day

Motorcycle riders in the desert
Image by Anja Knoche from Pixabay

On extremely hot days you may be able to smell gas coming from the exhaust or other parts of your bike. Hot weather can cause gas vapors to expand out of the tank or into other spots on the bike. The gas expands and if your fuel tank is to fuel the gas will need to go somewhere.

Whether it is vapors or fuel leaking into places it should not a fuel tank on a sweltering day is not a good idea. If it is exceptionally hot outside, it is a clever idea to not fill your tank full and then leave the bike to sit. This will allow the fuel to expand and can create leaks or damage.

The Float Needle Is Stuck Open

If your motorcycle is a carbureted bike, it will have a float needle. The float needle tells the engine how much gas should be flowing through the carburetor. As time goes on your bike will start to have a lot of buildup in the carburetor. 

To check if the float needle is stuck open you will need to:

  • Look at the bottom of your carburetor
  • Check the hole found on the bottom of the carburetor
  • If it is leaking fuel the float needle is open

If you are not sure if the carburetor is leaking, you will need to fully take apart the carburetor assembly. 

Spark Plugs Have Gone Bad

Motorcycle spark plug
Image by 2427999 from Pixabay

When spark plugs go bad several issues can happen as spark plugs are what is behind the powering of your motorcycle. If your sparkplugs go bad, they will not be able to ignite the fuel and air mixture which gives your engine power correctly.

Bad spark plugs can cause:

  • Bike to not start correctly
  • Engine flooding
  • Gas to leak out of your exhaust

If you notice your sparkplugs are darker looking than the light brown typical look, they have gone bad and need to be thrown away.

An Exhaust Smelling Like Gas Can Be Several Things

Fuel smells coming from your motorcycle are important and need to be checked. When you can troubleshoot issues that may happen with your motorcycle you will save time and money. Mechanics typically charge to diagnose the issues before even fixing the bike. It is also a particularly clever idea to know about the issues of your motorcycle that will help you to diagnose any future problems.

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