Dealing with gas leaks on a motorcycle is a hassle. It’s somewhat common among older motorcycles, but can surprisingly happen to new motorcycles as well.
Not only is it annoying, but motorcycle gas leaks can also be dangerous. You may have noticed your motorcycle has started doing it and you may be left wondering how or where the gas leak is coming from.
So, why is my motorcycle leaking gas? Gas can leak from a motorcycle anywhere in between the motorcycle gas tank to the carburetor or fuel injector usually because a hose isn’t on tight, a gasket is worn, or a nut isn’t tight enough. The most common places a motorcycle leaks gas are the fuel petcock, the carburetor, holes in the gas tank, and the fuel injector.
It’s important to promptly take care of a motorcycle gas leak. Gas leaks can lead to exposure to toxic fumes, gas on your clothes, wasted money, and further wear and tear on your motorcycle. I have owned over a dozen motorcycles and have been able to find the best ways to care for gas leaks that may happen.
Fuel Petcock
The fuel petcock (also known as the fuel valve) on a motorcycle is what controls the flow of the gas from the gas tank. This valve is either controlled with a butterfly handle or a ball valve
The most common place for a gas leak to happen on a motorcycle is the fuel petcock. The petcock can leak at any time, not just when you have it turned on for gas flow.
Petcocks more commonly leak from a faulty gasket that connects the petcock to the bottom of the gas tank. They can also leak from the internal mechanism it has because it has little gaskets and o-rings that can become brittle over time. This will cause gas to come out from the body of the petcock itself. Again, these types of leaks can happen whether you have it in the reserve, on, or off positions.
This can easily be diagnosed. Locate the petcock on your motorcycle and see if you notice any seepage coming from it; the leak can happen whether or not the motorcycle is on and running.
If you suspect the gas leak is from the petcock but not sure if it’s the gasket or the petcock itself, try replacing the gasket that goes between the petcock and tank first since it’s an easy fix. Completely empty the gas tank and disconnect the petcock from the tank (you can learn how to completely empty your motorcycle gas tank by reading our other article here). Replace the small gasket that goes between the petcock and the gas tank. You should be able to get the right part at an auto store or online for a few dollars.
Some petcocks don’t have a gasket. Instead, some have the petcock threaded in to the gas tank. If this is the case for you, get some fuel-resistant gasket maker and put it inside the thread to get a leak-free, tight fit. Make sure the gas tank is empty when you use fuel-resistant gasket maker and let it sit for 24 hours to cure before adding gas to the tank.
If you notice the leak is coming from the bottom of the petcock, it’s likely that the hose clamp is not tight enough. This is also an easy fix and only requires you to tighten the clamp around the hose.
If you have tried the previous methods and neither worked, or you suspect a faulty internal petcock leak, you’ll simply need to get a new petcock. Luckily these are fairly inexpensive. Make sure the seal to the petcock and gas tank are tight as well as the hose clamp on the bottom of it when you replace the whole part.
Carburetor
The carburetor on a motorcycle is what delivers the proper air and fuel ratio the engine needs to combust and make the engine power the motorcycle.
The second most common place you’ll have a gas leak on your motorcycle is the carburetor. The biggest reason a carburetor will leak gas is if the gasket that sits on top of the carburetor bowl is brittle or worn. This bowl on the carburetor is what holds gas that is getting prepared to be sucked into the engine. With the gas sitting there, it’s easy for the gas to leak if the gasket isn’t doing it’s job.
Luckily, these gaskets used on top of the bowl of the carburetor is pretty inexpensive, I can usually find the ones I need online for only a few dollars. You will need to take the carburetor off the motorcycle and take it somewhat apart to put the new gaskets in
The bottom of this bowl on the carburetor has a drain plug that is also susceptible to leaking gas. Sometimes these plugs become lose, usually from the vibrations of the motorcycle. Make sure that drain plug is tight so fuel won’t leak out of it.
Carburetors can also leak from the fuel connection, meaning the leak could be the connection between the fuel line to the carburetor. This is a matter of a loose hose clamp so make sure that is tight.
If you have a 2, 3, or 4 cylinder bike, you’re carburetors are going to be connected (essentially each cylinder has it’s own carburetor). Sometimes there’s a fuel bar that goes between the carb banks. These fuel bars have to have an o-ring on both sides. For example, between carbs 1 and 2 there’s going to be two o-rings, between 2 and 3 there’s going to be two more and so forth.
If any of these o-rings are bad, fuel is going to leak out between these carb banks. So if you notice a gas leak somewhere in the middle between two carburetors on your motorcycle, shine a light up inside the carburetor and determine between which carb bank the leak is. Then take your whole carburetor off, take it apart, and look for a broken o-ring in between the two carb banks where you identified the leak.
If you’ve determined that all the o-rings between the carb banks have become worn, replace all of them.
I have created a video series about restoring motorcycles from start to finish and within this series includes a detailed 25 minute video on how to clean and rebuild carburetors. This series also includes other hard-to-tackle components such as body work and electrical. I give dozens of tips and tricks that you won’t find anywhere else online. Click here for more information if you’re interested in viewing multiple videos that will help fix up your bike or if you’re interested in completely building your dream motorcycle!
Holes In The Gas Tank
We’d like to think that because of the material a motorcycle gas tank is made out of, the only thing they’d be susceptible to is dents. Unfortunately, gas tanks can form holes in them which could be the cause of your motorcycle gas leak.
Holes in the gas tank are usually caused by rust but can also form if there’s a lot of wear on it (such as if it was dropped hard or dragged across asphalt). Older motorcycles are especially susceptible to holes in the gas tank and living in humid places increases the chances of it.
If you notice gas leaking all over, your likely culprit is a hole in the gas tank. This will be a constant leak whether or not the motorcycle is on. Because there are several parts underneath the gas tank, the place of the leak can seem random.
To locate the exact place of the hole in the tank if it is not easily seen, you need to slightly elevate the tank off the motorcycle with it still connected to the fuel lines. Dry everything underneath so when the leak forms, you’ll able to easily locate it.
If you do have a hole in your motorcycle gas tank, you’ll simply need to get a new one. Do not attempt to fix the hole yourself with a filler or by welding it. Welding it can cause an explosion. If you absolutely have to have it welded, take it to a professional who knows how to deal with that.
Fuel Injector
Fuel injectors have been common on motorcycles for the last 10 years. They have proven to work well in delivering the right air and fuel ratio the engine needs to the power the motorcycle. Having a gas leak from the fuel injector is the least common and least likely reason your motorcycle is leaking gas, but it is still possible.
Within a fuel injector, you have a fuel rail and injectors with o-rings on them. For the most part these parts are durable and usually don’t have any problems with leaks. However, if you’ve been taking these parts in and out several times or if you’ve been working on the fuel injector, a gas leak can be quite possible.
You can detect if the fuel injector is your problem by examining it. It is usually located on the back side of the engine (usually where you would find a carburetor). Examine it for any leaks.
Fuel injectors are a lot more complicated than carburetors because it’s an electronic system. So if you suspect your fuel injector is the reason your motorcycle is leaking gas, you’ll either need to take it in to a mechanic or get a new fuel injector altogether.
Related Questions
Why is my motorcycle running rich? A motorcycle may run rich because the air to fuel ratio needs to be adjust, the needle is sticking to the carburetor, stuck open floats, a dirty air filter, butterfly valves that are stuck open, and the 02 sensors need to be changed if your motorcycle has them. Click here to see my article for more info.
Why is my motorcycle backfiring? A motorcycle backfire happens because of the presence of uncombusted fuel in the exhaust pipe. This issue is caused by incorrect timing, too much fuel, loose exhaust pipe, too short of exhaust, too little fuel, and intermittent spark. Click here to see my article for more information.