4 Reasons Your Motorcycle Is Leaking Gas And How To Repair

Fuel leaks are a dangerous nuisance that need to be addressed promptly to avoid catastrophic damage. There are many very hot components on a motorcycle that if fuel were to spill onto could potentially catch fire.

This is an issue that can happen to any motorcycle but is more common in older models with more worn components. Gas leaks can expose the rider to nasty fumes, ruin clothing, or spill on the ground and cause an accident.

If you have ever been riding and smelled raw fuel, the first thought through your mind was probably 1. Where is the source of the leak? and 2. How do I go about making a repair?

In general, fuel leaks on modern motorcycles can be isolated to either the gas tank, gas lines, or injectors. On older models the petcock and carburetor are more than likely the cause. Parts that are common to fail are gaskets, hardware, or material.

The sections listed below address good areas to begin a diagnostic and techniques to make a good repair that will last and not leave you stranded. If you have an older carbureted engine, I recommend starting with sections 4 and 5 then moving back up the list.

1. Gas Tank

The first component I would inspect after you have identified a fuel leak is the fuel tank. Depending on the condition and age of the bike, this inspection will go fairly quickly and lead you to a logical next step.

Even though fuel tanks are typically constructed from robust materials like metal or plastic, they can develop leaks over time.

Motorcycle gas tanks can leak if they have been damaged by an impact or exposed to the elements to the point of forming rust and wearing through. The latter condition is more common on older motorcycles with metal tanks. They also have a weak spot on the underside where the fuel pump mounts and is sealed by a rubber gasket.

Diagnosis

The best way to identify a tank leak is if the bike leaks all the time whether it is running or off. If this is the case, and the leak seems to be originating from that general area, this is the best place to start.

I would recommend unbolting the front hardware by the triple clamp and lifting the tank up with the rear hinge bolt and fuel pump with lines still attached. Make an initial inspection and determine any obvious sources.

If there aren’t any obvious rust spots that have worn through and no damage, the next step is to move onto the fuel pump.

Most modern bikes have an assembly bolted onto the bottom of the tank that serves two purposes.

  1. Hold the fuel pump which feeds fuel from the tank to the engine.
  2. Hold the fuel level sensor to indicate fuel level inside the tank.

This housing is sealed to the tank with a simple rubber o-ring that can fail at will.

Repair

At this point with the tank partially removed at an angle on the hinge bolt, go ahead and fully remove the tank by removing the seat and removing the final bolt.

IMPORTANT NOTE: The fuel should have been emptied from the tank by this point ideally by siphoning into a secondary container.

Otherwise, fuel will spill out everywhere in the next step

Removing the fuel pump housing will prove to be easy at this point by removing the hardware. The rubber o-ring slides down the top of the assembly and mounts against a flange that adjoins with the tank. No special tools or parts are required for this repair just a new gasket.

At this point your have two options:

  1. Reassemble the tank and remount onto the bike to recheck for a fuel leak.
  2. Since you already have the bike apart continue onto the second step to take additional precautions.

2. Gas Lines

Fuel lines come in a variety of materials and can be mounted in multiple ways depending on what bike you have. We will go through the variants and come to a solution regardless of what motorcycle you have.

We’re picking up this section from the end of item 1, so if you jumped straight here you need to dismount the fuel tank and remove the fuel pump housing. The fuel lines can attach to the assembly either by means of a fitting or a bolt.

In general, motorcycle fuel lines leak either because of a failed fitting, faulty gasket, or split line.

Diagnosis

First we will diagnose a rubber fuel line attached to a fitting. Fittings can either thread into the tank or have a quick disconnect attachment. They can also be metal or plastic. Most fuel lines are rubber but some can be steel braided.

In the case of a rubber line, always check first for cracks in the rubber or somewhere it may have been bound or split. This is especially important on an older bike where the rubber is old and dry which would make it more susceptible to cracking.

Regarding plastic fuel fittings, we are looking for a potential crack that is letting fuel to escape. This might be a very small crack, so a useful test would be to cap off all ends but one and force fluid through the other end to expose a failure.

For metal fittings, corrosion is going to be the most likely culprit. Inspect for any rust and surfaces that don’t align properly that may let fuel through. Additionally, fuel may be escaping past the threads going inside the tank.

It wouldn’t be a bad idea at this point to use some thread sealer when reinstalling a good metal fitting back into the tank to prevent a leak from the threads. Really cheap from any local tool store.

On some fuel tanks, a metal bolt called a banjo bolt threads into the tank and has a metal fuel line that it slots through to allow fuel to pass from the tank to the engine.

In this scenario you might run into some gaskets that fail as well as the bolt itself and line assembly altogether. Based on visual inspection alone, if this system looks corroded and old just get all new parts.

3. Fuel Injectors

This can be one of the more devastating issues to have on this list because of the potential catastrophic consequences. Fuel injectors serve the purpose of spraying fuel into the combustion chamber to be ignited and combused.

The reason this can be such a problem is that a leaking injector can lead to gas mixing with your engine oil. Gas is not a lubricating liquid, so if it mixes with your oil and “thins” it out, your engine will have reduced lubrication and not last long.

Diagnosis

Some symptoms to look out for in the instance you have leaking injectors are reduced fuel economy, rough idle, and difficulty starting when hot. You should also notice the smell of fuel after operating the bike.

You won’t, however, notice any fuel leaking externally like with a leaking tank because the failure is inside the engine.

The only reason you should be on this step is because you performed the first two steps in the diagnostic chain successfully and still have issues that can be traced to a fuel leak.

The fuel injectors on a modern motorcycle will be mounted to a fuel rail which is fed high pressure fuel by the fuel pump in your tank. You would be best served to remove the tank and airbox to gain access to the top and back of your engine.

Once you identify the location of the injectors, you will need to remove them and assess the health of the o-ring seals and the body of the injector.

This is a similar situation to the one we discussed above: since everything is apart do we just replace everything or do you start with the cheapest logical failed part and work through the process to save money.

Good news is a failed rubber o-ring is easy to identify and very cheap to replace so that should be done regardless. You can test all four injectors by leaving them on the fuel rail and actuating the pump to spray fuel and determine if a failure is present.

Repair

This is a simple parts replacement once the diagnosis is complete. No special tools or materials are required, but be careful when pressing in the injectors to make sure not to pinch or roll the o-rings to make sure they make a good seal.

Also, if you did indeed have this failure with your injectors, make sure you either run some fuel system cleaner through your fuel system periodically or perform a fuel injector cleaning at your major service maintenance interval.

4. Evolution Of Motorcycle Technology

Over the past few decades, there have been substantial leaps in motorcycle technology. Quick shifters, wheelie control, traction control; the list goes on about how modern bikes can hardly be compared to something built pre-2000.

One advancement pertinent to this topic of fuel leaks is the move from carburetion to fuel injection. The older technology had some different issues than we have discussed thus far.

Older carbureted bikes are typically equipped with a fuel petcock which is used to turn the fuel on or off. The carburetor itself has many little gaskets and o-rings to keep the fuel where it needs to be. If a bike has been sitting for a long time, the gaskets will get brittle and fail causing an oil leak.

Ride With Leaking Gas?

Under no circumstances should you be operating a motorcycle with an active fuel leak. You will either catch yourself on fire, blow your engine up, or if you’re lucky, simply run out of gas.

Most fuel leaks are fairly simple repairs in the grand scheme of things and don’t require any special training or tools.

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