Motorcycle Reserve Fuel Switch: The Beginner’s Guide

Motorcycle Reserve Fuel Switch, also known as fuel petcock valve, or simply fuel valve, is one of the motorcycle’s most basic and significant components. It controls the flow of fuel from the tank to the engine and lets you manage the fuel movement in your motorcycle.

If you are new to motorcycles or want to learn the operations of the fuel valve, then here is our beginner’s guide to the Motorcycle Reserve Fuel Switch. In this guide, we will discuss the purpose of the reserve fuel switch, all the valve positions, i.e., ‘OFF’, ‘ON’, and ‘RES’, and how to switch on your reserved tank.

Let’s get started.

Reserve Fuel Switch (Fuel Valve)

Reserve Fuel Switch or Fuel Valve is a small valve usually located on the left side of the motorcycle straight below the fuel tank, near the carburetor. It is a three-way valve with three switches, i.e., ‘OFF’, ‘ON’, and ‘RES’. You might find a fourth position such as PRI in some models, but these three are always available in all motorbikes.

The aim of the ‘On’ and ‘Off’ switches of the valve is to allow or stop the fuel movement from the tank towards the engine. The RES or Reserved switch, on the other hand, is related to using the reserved tank of the motorcycle. 

Every bike has a reserved fuel tank to store fuel in case the main fuel tank runs out of fuel. This ‘saved’ fuel is for when the vehicle needs to be driven to the nearest fuel station to refill the main tank. 

The reserve fuel switch is used to allow the movement of oil from your reserved tank to your carburetor and the engine and lets you ride the bike even when the main tank is empty.

Therefore, it is essential that you understand every movement and position of the fuel valve.

ON position

When you switch the reserve fuel switch to the ‘ON’ position, the fuel becomes free to flow from your main fuel tank to the carburetor and then to the engine. Hence, it is the position that you have to keep your reserved fuel switch when you are riding your motorcycle because if you don’t turn it ‘On’, your engine won’t receive the required fuel to start.

When the fuel from the main tank reaches the carburetor, it gets mixed with the air that leads to the formation of an air-fuel mixture. This air-fuel mixture travels from the carburetor to the engine combustion chamber and gets compressed and burnt with the spark plug of your bike. This burnt fuel is used to generate power in the engine and start your motorcycle.

Therefore, it is necessary to switch your reserve fuel switch to the ON position to start your motorcycle. 

OFF position

The next position of the valve is the ‘OFF’ position. If your motorcycle’s reserve fuel switch is in Off position, the fuel cannot flow to the carburetor and engine. You can use this position to cut off your fuel flow into the engine.

Usually, bikers keep their reserve fuel switched to OFF position when they are sure that they won’t be riding the motorcycle for a long time. However, some of the riders also switch their valves ‘off’ every time they park their motorcycles.

This type of aggressive switching OFF is not mandatory for you as a rider. However, we recommend you turn the valve OFF if you are not going to ride your motorcycle for the next two to three days. This way, your fuel won’t leave your fuel tank and you don’t have to bother about the unnecessary fuel going into your engine combustion chamber.

One thing that you should remember is that if your fuel is in the OFF position, you won’t be able to start your motorcycle as the engine won’t be receiving fuel to start.

Reserve Fuel Switch Positions

Reserve or RES is the fuel switch position when then stored fuel in the reserve tank can move to the carburetor and later to the engine of the motorcycle. As the name already suggests, this is the position where you can use your “Reserved” fuel when your main fuel tanks run out of fuel. 

One thing to notice here is that the reserved fuel tank is not a separate tank in your motorcycle. In reality, it is a part of the main fuel tank of your motorcycle. Therefore, you cannot use this fuel in the normal ON position. When you switch to the RES position, this stored fuel will start flowing to the carburetor and the engine.

One thing you must remember is that the fuel in the reserve tank is not for riding purposes. It is a backup solution to reach the nearest gas station and refill the main tank.

How To Switch To Reserve Tank In Motorcycle

Just imagine you are riding your motorcycle, the wind is gushing against your face, and you run out of gas in your fuel tank! These are the moments when the reserve tank comes as your lifesaver. Once you switch to the reserve tank, it will provide extra fuel flow to the engine and let you ride to the nearest gas station, and refill your main tank.

To switch to your reserve tank, all you have to do is find the fuel petcock valve on the left side of your motorcycle near the carburetor and turn it from the ON position to the RES position. You can simply turn it on by turning the valve by 180 degrees.

Once you turn the valve, the fuel from the reserve tank will start flowing into the engine and your motorcycle will start again.


Can I run my motorcycle on reserve all the time?

It is completely safe to ride your motorcycle on reserve all the time as it does not affect the functioning of the bike in any way. In fact, it is recommended to occasionally ride the bike in reserve fuel condition because when you ride your bike on reserve once in a while, it will allow the motorcycle to use fuel that is in the lowest part of the fuel tank. As a result, the dirt and crud will get out of the tank.

However, reserved fuel is a backup fuel option and once you consume this backup on the road, you are going to face trouble. This reserved tank is meant to take your bike to the nearest fuel station and if you keep your bike in low fuel condition all the time, you might run out of fuel and have to drag the bike.

What is the “PRI” position on the petcock?

Along with the On, Off, and RES positions, some fuel petcocks will also have the PRI position on their switch. This PRI  position on the petcock stands for prime and is used when you haven’t been riding the motorcycle for a long period and it has been running out of fuel. During such conditions, this PRI position is needed to fill up the carburetor.

This PRI position will allow the fuel movement from the tank to the carburetor even if your engine is not working at that time. Once you start the bike and the engine starts running, you should return the valve to its “ON” or “RES” position.

How long can I ride my bike with the reserved fuel?

When you switch on the reserve fuel, you can usually ride the bike between 20 to 50 miles.

Why do some bikers always turn off the reserve switch whenever they park their motorcycle somewhere or just park it in the garage for the night?

The main reason to switch off the fuel valve is to stop the unnecessary flow of oil from the tank to the carburetor. This keeps your carburetor in a healthy position.

Apart from that, many riders feel that the fuel tank is above the engine, and if the fuel somehow leaks from the rubber supply hose, it will drip on the hot engine. So, they switch it off whenever they are not using their bike.

Why do some people ride their motorcycles with the fuel switch always on “Reserve”? 

When riders are going at a high speed and the tank runs out of fuel, the bike will feel an unwanted stutter and stop in the middle of the road. On the contrary, if the reserve is on, the fuel will continue to flow from the tank to the engine and the bike won’t stop all of a sudden.

This is usually practiced by experienced riders who don’t want their bikes to stop and know how much their bikes will run in the reserve fuel.

How much fuel is in the reserved tank?

Most of the time, there are specifications near the fuel tank about the reserved tank and you also see a red warning light when you run on low fuel. There are no general specifications about the capacity of the fuel tank but usually, 10-15% of the fuel of your main tank’s capacity is stored in the reserved tank.

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