Mercedes Mullins
The number of breathers on a motorcycle fuel tank varies depending on the make and model of the motorcycle. Some motorcycles have a single breather tube/hose, while others have two. The purpose of the breather tube/hose is to vent the tank, allow excess fuel to overflow, and prevent fuel spillage in the event of an accident. Some motorcycles also have a separate vent tube with a breather filter to prevent fuel leakage. In some cases, a catchcan is used to collect fuel overflow, especially when riding hard or during heavy braking. The breather system plays a crucial role in ensuring the safe and efficient operation of the motorcycle's fuel system.
Motorcycle Fuel Tank Breather Characteristics
| Characteristics | Values |
|---|---|
| Purpose | To vent the tank, allow excess fuel to overflow, and close off the flow of gas out of the tank in the event of an accident |
| Types | Vent tube, breather valve |
| Vent Tube Length | 3 inches to 3 feet |
| Breather Valve Length | 1 inch |
| Breather Valve Functionality | One-way valve that shuts off if tipped over |
| Additional Considerations | Use of a catch can under the fuel tank overflow/vent hose to prevent fuel from sloshing out during hard braking |
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What You'll Learn
Breather valves can get blocked, causing issues
Breather valves on a motorcycle fuel tank can get blocked, causing issues. This can happen due to a build-up of residue or debris, or even water ingress. Blocked breather valves can result in fuel starvation issues, as experienced by some riders in the rain. This is because the breather system acts as an overflow when the fuel expands due to heat, and if the valve is blocked, fuel may be unable to flow through it.
One way to clear a blocked breather valve is to remove it and shake it vigorously to dislodge any debris or residue. In some cases, it may be necessary to replace the valve if it is severely blocked or damaged. It is important to refer to the owner's manual for specific instructions on clearing and maintaining breather valves, as they play a crucial role in preventing fuel spillage and reducing the risk of fires.
Additionally, water blocking the breather hose can cause issues. A "slash cut" technique can be used to prevent this issue, although the scientific reason behind it is unclear. This technique involves making a long slash cut on the end of the hose where it exits by the swing arm pivot area. This is a common issue on California models, where the hose terminates in an EVAP charcoal canister.
Blocked breather valves can also cause vacuum problems, as experienced by a rider on a Triumph motorcycle forum. In this case, the gas cap would not open due to the suction created by the blocked valve. Clearing the blockage or replacing the valve can resolve such vacuum issues. It is important to regularly inspect and maintain the breather valves to prevent blockages and ensure the safe and proper functioning of the motorcycle fuel tank.
Furthermore, the roll-over valve, a critical component of the breather system, can become faulty. This can happen if the ball inside the valve gets stuck in the closed position due to overfilling the tank beyond the recommended level. Regularly following the owner's manual instructions can help prevent this issue. A blocked or faulty roll-over valve can lead to fuel overflow and spillage, potentially causing safety hazards.
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Vent tubes can leak fuel if the motorcycle falls
A motorcycle fuel tank typically has one or two breather tubes, also known as overflow fuel tubes or vent tubes. These tubes serve multiple purposes, including venting the tank, allowing excess fuel to drain, and preventing fuel spillage in the event of an accident.
While these vent tubes are designed to prevent fuel spillage, it is possible for them to leak fuel if the motorcycle falls. This can occur due to several factors, and understanding the causes can help address the issue effectively. One common reason for fuel leakage from vent tubes is a full tank of gas. When the tank is filled to the brim, there is little to no space for the fuel to expand, especially if the motorcycle is left in the sun or exposed to heat. As the fuel warms up, it expands, creating additional pressure that can force fuel out through the vent tube, resulting in a drip.
Another potential cause of fuel leakage from vent tubes is a faulty or damaged roll-over valve. The roll-over valve, also known as a tip-over check valve, is designed to block the outflow of fuel if the motorcycle falls or is laid on its side. If this valve becomes stuck in the closed position or malfunctions, it can fail to prevent fuel spillage when it is most needed. Regularly overfilling the tank beyond the recommended level can contribute to this issue. Therefore, it is essential to adhere to the owner's manual instructions regarding fuel levels to avoid such problems.
To identify the source of the leak, it is recommended to inspect the vent hoses and fuel fittings. In some cases, the vent hoses may become loose or detached, leading to fuel leakage. Additionally, broken or cracked fuel fittings can result in fuel dripping from the vent tube. It is advised to carefully examine these components and, if necessary, replace or repair any damaged parts. Furthermore, carburetor issues, such as clogs or malfunctions, can also lead to fuel leakage around the air channels, emphasizing the importance of regular maintenance and proper care of the motorcycle's fuel system.
To address fuel leakage from vent tubes, several solutions can be considered. One suggestion is to use a catch can under the fuel tank overflow/vent hose. This catch can collect any fuel that may spill, preventing it from reaching the ground or the hot engine components. Additionally, ensuring that the vent hoses are properly attached and in good condition can help mitigate the risk of fuel leaks. If the issue persists, it may be necessary to consult a professional technician to diagnose and resolve any underlying problems contributing to the fuel leakage.
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A catchcan can prevent fuel from spilling out of the breather line
A motorcycle fuel tank typically has one or two breather tubes, also known as overflow fuel tubes. These tubes are designed to prevent fuel from spilling out of the tank in the event of overfilling or when the bike is laid on its side.
While breathers help prevent fuel spills, they don't always work perfectly. In some cases, fuel can still spill out of the breather line, especially when the tank is more than three-quarters full and the bike undergoes heavy braking or acceleration. This can create a dangerous situation, as fuel spilling onto a hot engine or tyre can pose a fire risk.
To address this issue, some motorcycle owners opt to use a catch can, which is a small container that captures any fuel that might escape through the breather line. By placing the end of the breather hose into the catch can, riders can prevent fuel from spilling out onto the bike or the ground. This simple modification can provide added peace of mind, especially when riding aggressively or taking corners at high speeds.
Additionally, catch cans can help prevent fuel odour from lingering on the bike and its components. Spilled fuel can be difficult to clean up completely, and the smell of gasoline can persist even after the visible traces have been wiped away. By containing spills, catch cans help keep the bike cleaner and less likely to attract unwanted attention from the lingering scent of gasoline.
In conclusion, while breathers play a crucial role in preventing fuel spills, adding a catch can provides an extra layer of protection. This inexpensive modification can help riders avoid dangerous fuel spills, reduce fire risks, and maintain a cleaner, better-smelling bike. It is a worthwhile consideration for any motorcycle enthusiast looking to enhance the safety and cleanliness of their machine.
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Gas caps have no breather hole to prevent fumes escaping
Gas caps play a crucial role in sealing your fuel tank and preventing fuel vapors from escaping. Older vehicles used to have vented gas caps, which were essentially gas caps with a hole that allowed fuel to splash out during acceleration or turning corners. However, modern safety and emission laws prohibit gas caps from venting raw gas fumes into the atmosphere.
To comply with these regulations, modern gas caps have no breather hole at all. Instead, they feature a spring-loaded valve in the centre, known as a blow-off valve. This valve remains closed under normal conditions, preventing fumes from escaping. However, if the gas tank becomes pressurised due to expanding gas and fumes, the blow-off valve opens to release the pressure. This design ensures that gas fumes are not released into the atmosphere during everyday use.
The absence of a breather hole in gas caps also helps to reduce fuel evaporation and improve fuel mileage. By preventing vapors from escaping the gas tank, more fuel is retained for engine use. Additionally, the sealing function of the gas cap plays a crucial role in sealing the evaporative emissions (EVAP) system, which manages fuel vapors within the fuel system and the engine.
While the lack of a breather hole effectively prevents fumes from escaping, it can lead to pressure build-up in the fuel tank under certain conditions. For example, in hot weather or extreme climates, the expansion of fuel due to heat can cause pressurisation. In such cases, the blow-off valve may activate to release the pressure, but it is designed to open only under specific pressure conditions.
Some individuals choose to modify their gas caps by drilling holes in the valve to provide additional ventilation. However, this practice is not recommended as it defeats the purpose of the emission control design and can lead to environmental concerns by allowing fumes to escape into the atmosphere.
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Roll-over valves prevent fuel spillage and fire risk
The number of breathers on a motorcycle fuel tank varies. For instance, the 2008 Versys has one breather tube, while the Ninja 2009 650r fuel tank has two.
Motorcycle fuel tanks are equipped with roll-over valves to prevent fuel spillage and the risk of fire. These valves are designed with a ball that blocks the outflow of fuel when the motorcycle is laid over on its side or upside down. This mechanism stops the flow of fuel, preventing it from spilling out of the vent tube and creating a dangerous situation.
The correct orientation of the roll-over valve is crucial for its proper functioning. When the motorcycle is sitting normally, the valve should be positioned beneath the fuel cell. In the event of a rollover, the valve will then be above the fuel level, preventing any fuel from leaking through.
It is important to note that the roll-over valve also serves as a fuel cell vent, allowing fuel to flow out of the fuel cell so that the motorcycle can operate. This vent needs to be open when the motorcycle is on a level surface and will close when the vehicle is rolled over, further ensuring that no fuel spills out.
The roll-over valve is an essential safety feature that helps to prevent fuel spillage and the risk of fire in the event of a motorcycle accident or rollover. By blocking the outflow of fuel, this valve contributes to a safer riding experience and reduces the potential for fuel-related fires.
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Frequently asked questions
A breather on a motorcycle fuel tank, also known as a vent tube or a breather valve, is used to vent the tank and prevent it from becoming pressurised by expanding gas and fumes. It also allows excess fuel to overflow and close off the flow of gas if the bike is laid over to prevent fuel spillage and the risk of fire.
Yes, there are two main types of breathers for motorcycle fuel tanks: vent tubes and breather valves. Vent tubes are typically longer and can range from 3 inches to 3 feet in length. Breather valves, on the other hand, are shorter and usually stick up about 1 inch from the tank.
Vent tubes are longer and may be more cumbersome, but they are less likely to get gummed up compared to breather valves. Breather valves are more compact and less obtrusive, but they may be more prone to getting clogged over time. It's worth noting that both types serve the same function and many people may not notice a difference between the two.
You can identify the type of breather on your motorcycle fuel tank by examining its appearance. Vent tubes are longer hoses that extend from the fuel tank, while breather valves are shorter and typically stick up about an inch from the tank. You can also refer to your motorcycle's user manual or seek advice from a mechanic or motorcycle forum.
It is important to regularly inspect and maintain your motorcycle fuel tank breather to ensure its optimal function. For vent tubes, ensure there are no obstructions or blockages in the hose. For breather valves, check for any debris or dirt that may have accumulated and clean or replace the valve if necessary. Additionally, consider using a filter to keep dirt and debris from entering the breather system.
