Motorcycle Fuel Petcock Replacement: A Step-By-Step Guide

The fuel petcock, or fuel shut-off valve, is a simple but essential component of a motorcycle's fuel system. It allows the rider to control the flow of gasoline from the gas tank to the carburetor, with settings for on, off, and reserve. The on position is used during normal operation, providing fuel to the engine. When the fuel level drops, the engine starts to sputter, and the rider switches to the reserve setting, which accesses the remaining fuel in the tank. The off position is a precaution to prevent fuel leakage when the motorcycle is not in use.

In this discussion, we will explore the process of replacing a motorcycle fuel petcock, including the tools and parts required, step-by-step instructions, and troubleshooting tips. We will also discuss the different types of fuel petcocks available and how to choose the right one for your motorcycle.

Understanding the function of a motorcycle petcock

A motorcycle petcock, or fuel petcock, is a small shut-off valve that controls the flow of gasoline from the gas tank to the carburetor. The term comes from the two words: "pet", which means "small" in French, and "cock", which means "to block" or "stop".

Most older motorcycles have a three-position fuel petcock valve: on, off, and reserve. The on position allows access to most of the tank, with a little left in reserve. When the fuel drops below a certain level, the engine will sputter and start to die. This is when the reserve position comes in handy, as it allows access to the bottom portion of the tank, giving you enough fuel to get to the nearest gas station. The off position is a precaution to prevent fuel leakage when the motorcycle is not in use.

Some petcocks also have a "prime" position, which is used for vacuum-operated petcocks when the motorcycle has run out of fuel before filling up. It allows fuel to flow freely and fill the carb bowl.

When choosing a petcock, it is important to consider the direction in which the petcock outlet needs to face (left, right, or vertical) as well as the size of the fuel inlet and the thread pitch and size for the petcock bung on the gas tank.

A reliable fuel petcock valve is essential for optimal fuel flow control and efficient performance of your motorcycle's fuel system.

Choosing the right petcock size for your motorcycle

Petcock Outlet Direction:

The first step in choosing the right petcock size is determining the direction in which the petcock outlet needs to face. This could be towards the left side, right side, or vertical. This factor will help narrow down your options and ensure the petcock aligns with your motorcycle's fuel system design.

Fuel Inlet Size:

You'll want to match the size of the petcock's fuel inlet with the size of your motorcycle's fuel line. The fuel inlet size is usually measured in inches or millimetres. Common sizes include 1/4 inch, 3/8 inch, and 22mm. Ensuring the fuel inlet size matches your fuel line will guarantee a proper fit and optimal fuel flow.

Thread Pitch and Size:

Another critical measurement to consider is the thread pitch and size of the petcock bung on your gas tank. The thread pitch refers to the distance between each thread, and it needs to match the pitch on your gas tank for a secure and proper fit. A mismatch in thread pitch or size can result in fuel leaks or improper installation.

Motorcycle Model and Type:

Different motorcycle models and types may require specific petcock sizes. For example, late-model Harley-Davidsons typically use a 22mm petcock, while custom and aftermarket gas tanks may use smaller sizes like 1/4 inch or 3/8 inch NPT (National Pipe Thread). Check with your motorcycle's manufacturer or a trusted mechanic to determine the recommended petcock size for your specific model.

Adapter Nuts:

If you're having trouble finding a petcock that fits your gas tank directly, adapter nuts can be a solution. Lowbrow Customs offers adapter nuts in brass and chrome that allow you to use a 22mm petcock bung with a 1/4 inch or 3/8-inch NPT petcock. This can provide more options for your motorcycle and help you find the perfect fit.

Remember, choosing the right petcock size is essential for the safe and efficient operation of your motorcycle. Always refer to your motorcycle's manual or seek advice from a professional if you're unsure about the correct petcock size or type for your specific model.

When to switch your motorcycle petcock to on

Knowing when to switch your motorcycle petcock to 'on' is essential to your safety and the performance of your bike. Here are some detailed guidelines on when to do this:

When Riding:

The "on" position on your motorcycle petcock is for normal operation and should be used whenever you are riding your bike. It allows fuel to flow from the tank through the top portion of the petcock and down to your fuel system. When the bike is running and the fuel level drops below the "on" tube, the engine will start to sputter and may die.

When Refuelling:

After refuelling your bike, always return the petcock to the "on" position. This will give you access to most of the tank, with a little left in reserve.

When Running Low on Fuel:

If you are riding and your bike starts to sputter due to low fuel, switch to the "reserve" position. This will allow you to access the remainder of the fuel in your tank, which should be enough to get you to the nearest gas station.

When Performing Maintenance:

If you need to drain the fuel system while the engine is running, for maintenance purposes, switch the petcock to the "off" position.

When Parking:

It is recommended to switch your petcock to "off" when you are not riding your bike, especially if you are parking overnight or for extended periods. This will prevent fuel from leaking and causing potential damage to your bike's engine.

Remembering to switch your petcock to the correct position is crucial for a safe and enjoyable riding experience. By following these guidelines, you can ensure that your bike has the proper fuel flow and that you don't accidentally run out of fuel during your rides.

When to switch your motorcycle petcock to reserve

The "reserve" setting on your motorcycle's petcock allows you to draw fuel from the bottom of your gas tank. During normal operation, you should set your petcock to the "on" position, which allows fuel to flow from the tank through the top portion of the petcock. When the fuel level drops below this point, your engine will sputter and start to die. This is when you should switch to the "reserve" setting, which will allow you to use the remaining fuel in your tank and, hopefully, reach the nearest fuel station.

It is recommended to switch to the "reserve" setting before you start riding if you are unsure whether you have enough fuel to complete your journey. This will help prevent you from running out of fuel in the middle of your ride.

Some riders avoid using the "reserve" setting due to concerns about introducing dirty fuel into their carburettors. However, others believe that using "reserve" provides a better path to constantly clean fuel. Additionally, using the "reserve" setting periodically can help minimise the issue of water layering at the bottom of the tank.

It is also important to note that if you have a manual petcock, you should get into the habit of turning it to the "off" position when shutting off the engine. This will reduce the risk of fuel leaks during non-use and help prevent potential fire hazards.

When to switch your motorcycle petcock to off

It is recommended that you switch your motorcycle petcock to 'off' when your bike is parked, or when it is not in use. This is because, if you leave the petcock 'on', you are relying on the carburetor float valves to shut off the fuel flow. If these valves fail, or get some dirt in them, fuel can leak out, creating a fire hazard. This can also result in fuel getting into the crankcase, which can cause serious engine damage.

If you are only stopping for a short period of time, such as a few hours, it may not be necessary to switch the petcock to 'off'. However, it is generally good practice to get into the habit of switching it off every time you stop riding, as this will help to prevent leaks and engine damage.

It is also important to switch the petcock to 'off' if you are storing your bike for a long period of time, or if you are transporting it. This will help to ensure that the fuel system is empty and reduce the risk of leaks during storage or transport.

Additionally, if you are running low on fuel and need to switch to the 'reserve' setting, it is a good idea to switch back to the 'on' position once you have refuelled. This will help to ensure that you do not accidentally run out of fuel again while riding.

Frequently asked questions