The purpose of the reserve tank is to act as a safety net for riders giving them a heads-up warning that they are running low on fuel.
It is a very simple concept but one that can raise a lot of questions sometimes.
Not all motorcycles have a reserve fuel tank. Most FI (Fuel injected) motorcycles do not have a reserve tank. However, carbureted motorcycles usually have a reserve tank. Some motorcycles can have a fuel gauge or a low fuel light instead of a reserve tank.
This means that your motorcycle may not really have a reserve fuel tank, and that should not be considered a cause for concern.
Below I go more in-depth about what you should know about your reserve fuel tank.
Table of Contents
Why do motorcycles have a reserve?
The purpose of the reserve fuel tank in motorcycles is to serve as a low fuel warning. When the fuel in the main fuel tank gets too low, the motorcycle will start to sputter, notifying the rider to switch to the reserve tank and look for a fuel station to refill their tank.
How reserve works
The reserve tank is not a separate fuel tank from the main fuel tank. The reserve is a part of the main fuel tank. The reserve tank should be considered to provide a low fuel warning similar to the fuel gauge or the low fuel light some motorcycles have.
Usually, inside the fuel tank, there are two outlets of a different length through which the fuel can flow from the fuel tank and into the engine. When the fuel gets low enough to get just below the longer outlet, the rider will have to switch to the lower outlet, which is the reserve. See the image below for an exemple.
Once the fuel gets too low in the main fuel tank, the rider has to switch to the reserve in order to use the rest of the fuel in the fuel tank. That way, they know they are left with just enough fuel to get them to a fuel station.
If you are interested in knowing how much time you have to find a fuel station after switching to the reserve, read my article about how far motorcycles can go on reserve, where I give you some real-world numbers and examples.
Running on reserve
So what will happen if we run the bike in reserve mode when the tank is full?
Since the reserve is part of the main fuel tank, this means that riders can run the motorcycle on reserve all the time, even if the tank is full. Nothing bad will happen to the motorcycle, but the downside is that the rider may not notice they are running low on fuel and get stranded on the road with no means of refueling.
I have gone into more detail about the possible dangers and downsides of running your motorcycle on reserve all the time in my article about what can happen if you run on reserve all the time.
Also, you do not have to worry about the reserve running out of fuel before the main tank or having to refuel the reserve tank separately. The main fuel tank and the reserve share the same space.
How to find out if your motorcycle has a reserve tank
Now in order to find if your motorcycle has a reserve, there are a few very easy steps that you can take.
Look for the fuel switch underneath the fuel tank
The easiest way to find out if your motorcycle has a reserve fuel tank is to look for the fuel switch (i.e., fuel petcock valve) located on the left side of the motorcycle under the fuel tank. Fuel switches usually have three positions, “ON”, “OFF”, and “RES”.
- For normal operation, the position of the petcock should be in the “ON” position, which allows the fuel from the fuel tank to reach the engine.
- Switching the petcock to the “OFF” position will prevent the fuel in the fuel tank from reaching the engine, which prevents the motorcycles from starting.
- Switching the petcock to the “RES” position allows the fuel in the reserve fuel tank to be used.
Here you can see a Harley Davidson Petcock With the following label:
- R = reserve
- On = fuel On
- Off = fuel Off
You can also see the height of the brass reserve tube on the right side of the petcock underneath the screening.
Some motorcycles will also have another setting called “PRI”, which stands for prime. This one is a little different and usually used after long-term storage, if the motorcycle has been tipped over, or after running out of fuel to fill up the carburetor.
Here you can see a DRZ400 petcock with the notion of PRI. Note that if you have to disconnect the fuel tank on this type of petcock, you must place the switch on PRI if you don’t want to drop fuel everywhere.
- Fuel = Fuel On
- PRI = Primer
- RES = Reserve
You can also clearly see the reserve tube in plastic and the fuel tube in brass. As explained earlier, if the fuel level is under the brass tube, you must place the petcock on RES. Since the reserve tube is lower, the car will now flow to the carburator.
If you have the fuel petcock on your motorcycle, this means that your fuel tank also has a reserve.
Check your motorcycle owner’s manual
Whether your motorcycle has a reserve fuel tank should also be noted in your owner’s manual detailing the capacity of the main fuel tank and the reserve fuel tank.
This is actually excellent information to know as it allows you to know how far your motorcycle can get on a full tank or after switching to the reserve.
If you are interested in some real-world data and comparisons, check my article on how far motorcycles can get on a full tank of gas. It can give you a good perspective of what you can expect on average from most motorcycles and what can affect the total distance traveled.
Check if your motorcycle has a low fuel light or gauge
Some motorcycles will have a low fuel light, gauge, or another means of displaying how many miles you have left before having to refuel.
If your motorcycle does not have a fuel petcock underneath the fuel tank, and nothing about a reserve fuel tank is mentioned in your owner’s manual, your motorcycle most likely does not have a reserve.
Why do some motorcycles not have a reserve?
Many of the older and carbureted motorcycles have a reserve because this is a very inexpensive way to be notified when the level of the fuel in the tank is getting too low.
Of course, there are other ways riders can keep track of how often they may have to fill up their motorcycles.
One of the most basic ways to do that is to figure out the fuel consumption of your motorcycle. Knowing your average MPG, which can be different from what the manufacturer has stated originally, you will know how many miles you can go on a full tank of gas. Then all you have to do is keep track of the distance you have traveled since your last refueling, which can be done using your trip meter or a GPS.
Today motorcycles may not really need to have a reserve tank anymore because there are alternative ways to keep track of how much fuel is left in the tank. Usually, today this is done by using a fuel gauge or a low fuel light.
Fuel gauges, low fuel lights, and reserve tanks are not 100% accurate all the time, but they are good ways to prevent you from running out of fuel in the middle of nowhere.
Now, if you are looking for tips and tricks on how to not run out of fuel, I recommend checking my article on how to not run out of fuel on your motorcycle.
Meet Simon, the 46-year-old aficionado behind YourMotoBro. With a lifelong passion ignited by motocross dreams and a Canadian Tire bicycle, Simon’s journey has been nothing short of extraordinary. From coaching underwater hockey to mastering muddy terrains, he’s an authority in thrill and adventure. Certified as an Off-Road Vehicle Excursion Guide and trained in Wilderness First Aid, Simon’s love for bikes is as diverse as his collection—from a robust BMW GSA R1200 to the memories of a Harley Davidson Night Train. By day a respected telephony consultant, by night a motorcycle maestro, Simon’s tales are a blend of expertise, resilience, and undying passion. ?️✨