How To Safely Adjust Your Fuel Cock Mid-Ride

The fuel petcock on a motorcycle is a 2-way or 3-way valve that controls the flow of fuel from the tank to the carburettor or fuel injectors. The primary reason for shutting off the fuel supply is safety. Since the fuel tank is usually above the engine, a leak could cause fuel to drip onto the hot engine, causing a fire. It is therefore recommended to turn the petcock off when the vehicle is not in use. However, some modern motorcycles have vacuum-operated petcocks that close automatically when the engine is off.

Safety reasons for shutting off fuel

The primary reason for shutting off the fuel on a motorcycle is safety. Here are some detailed safety reasons for shutting off the fuel:

• Fuel Leak: On a motorcycle, the fuel tank is typically located directly above the engine. If a fuel leak occurs, the fuel could drip onto the hot engine, potentially causing a fire or explosion.
• Rubber Supply Hose: Most motorcycles use a rubber supply hose to transport fuel from the tank to the engine. This hose is exposed to engine heat, which can cause the rubber to decompose over time, leading to leaks or cracks.
• Carburetor Float Valve: If the carburetor float valve leaks or gets stuck in the open position, fuel can continuously flow into the carburetor, causing an overflow. This excess fuel can then enter the cylinder and contaminate the oil, leading to potential engine damage.
• Hydraulic Lock: In older motorcycles with gravity-fed fuel systems, a manual shut-off valve is necessary to prevent fuel from continuously flowing into the carburetor. Without this valve, a hydraulic lock could occur, making it difficult to start the engine.
• Fuel Evaporation: Turning off the fuel when the motorcycle is not in use helps prevent fuel evaporation, ensuring that valuable fuel is not lost over time.

It is important to follow the recommendations in the user manual of your motorbike and always turn off the fuel when it is not in use to prevent potential safety hazards and maintain the proper functioning of your vehicle.

What happens if you leave the petcock on?

Leaving the petcock on can cause fuel to overflow into the carburetor, which can lead to a number of issues. Firstly, if the carburetor float valve leaks or gets stuck, gas will pour in and overflow, potentially running into the cylinder and seeping into the oil. This can cause a hydraulic lock, which can be catastrophic. Additionally, leaving the petcock on can result in fuel evaporating from the float bowl, leading to a build-up of gunk in the carburetor and float valve, which can then cause fuel to overflow into the engine.

Leaving the petcock on can also be a safety hazard. If the motorcycle tips over with the petcock on, fuel can leak out and cause a fire. Furthermore, if fuel leaks onto the hot engine, it can cause a fire or explosion. Therefore, it is generally recommended to turn off the petcock when the motorcycle is not in use, especially for longer periods or overnight.

Some modern motorcycles have vacuum-operated petcocks, which close automatically when the engine is off. In this case, it is not necessary to turn the petcock off manually. However, for older motorcycles with gravity-fed petcocks, it is important to turn them off to prevent fuel overflow and potential safety hazards.

Should you turn off the petcock?

The primary reason for shutting off the fuel on a motorcycle is safety. The fuel tank is positioned directly above the engine, so if fuel were to leak, it would drip onto the hot engine, causing a fire. This risk is heightened by the fact that most motorcycles use a rubber supply hose that is exposed to the engine's heat, which can lead to decomposition.

If the carburetor float fails to close the valve tightly enough to stop the fuel flow, and the petcock is left on, gas will continue to trickle into the carburetor. This can cause the carburetor bowl to overflow, with fuel flowing down into the intake tract and filling the cylinder. Then, when attempting to start the motor, the incompressible liquid gasoline will cause a catastrophic hydraulic lock.

Some modern motorcycles have a vacuum-operated fuel petcock, which closes when the engine is off. However, if the diaphragm fails, it could fill the crankcase with gasoline.

It is therefore recommended to turn off the petcock when the motorcycle is not in use, particularly if it is being stored overnight or in a garage.

What position should the petcock be in?

The petcock, or fuel tap, on a motorcycle has three positions: 'On', 'Off', and 'Reserve'. The 'On' position is used during the normal operation of the bike and is the position the valve should be returned to when refueling. When the bike is parked, the valve should be turned to the 'Off' position. This is a safety precaution to prevent fuel from leaking onto the hot engine and causing a fire. The 'Reserve' position is used when you run out of gas in the 'On' position. This will allow you to access the reserve fuel supply and should be used when the main supply is exhausted.

Some petcocks also have a Prime position, which is used to fill the carburetor when it is empty or after cleaning and reinstalling. It is important to note that leaving the petcock in the 'Prime' position can cause the carburetor to overflow, so it should not be left in this position for an extended period.

It is recommended to turn the petcock to the 'Off' position when the motorcycle is not in use to prevent fuel leakage and for safety reasons. Additionally, turning off the fuel can help prevent flooding of the engine, which can occur if the carburetor float fails to close the valve tightly enough to stop the fuel flow.

Can you run a bike on reserve all the time?

Running a bike on reserve means using the reserve fuel in the tank, which is meant for emergency situations when the bike runs out of fuel. While it won't harm the performance of the bike engine to ride it on reserve, it is not recommended to do so all the time.

The reserve fuel allows the rider to cover a few more miles to get to the nearest refuelling station. If the reserve is also drained, the rider will be left stranded with no safety net and no way of knowing when the main fuel tank was emptied. This could be a particularly challenging situation if the rider is on a long-distance trip and there is no fuelling station nearby.

One advantage of using the reserve fuel is that it can help to get rid of any dirt in the oil tank. When the bike is refuelled, dirt can settle at the bottom of the tank and accumulate over time, potentially choking the pipes and causing damage. Running the bike on reserve empties the tank and prevents dirt accumulation.

However, there are several disadvantages to running a bike on reserve all the time. Firstly, it defeats the purpose of having a reserve as an emergency backup option. Secondly, there is no indicator to show when the reserve tank is empty, so the bike could suddenly stop without warning.

Additionally, running on low fuel levels can put pressure on the engine, leading to wear and tear and potentially lowering the performance of the bike over time. These issues may not be covered by a bike insurance policy and could result in financial strain for repairs.

While it is not harmful to ride a bike on reserve occasionally, it is important to be mindful of the disadvantages and use the reserve fuel only in emergency situations, as intended.

Frequently asked questions