Motorcycle Only Runs On Reserve? Here’s Why


It’s Important for the fuel delivery system to work properly on every motorcycle. Though the fuel delivery system on motorcycles is simple, there can still be some issues that come along with it. One of those issues could include the petcock. Your bike may start to exhibit a weird behavior where it only seems to run while in reserve.

Why is my motorcycle only running while on reserve? A motorcycle may only run while on reserve because of a clogged petcock screen inside the fuel tank or the three-way valve on the petcock itself is clogged. Another less likely scenario is a failed vacuum line from the carburetor to the petcock. Ensure the vacuum line isn’t pinched shut or has a hole in it.

We’ve all ran into situations where you’re in the middle of nowhere, and you run out of gas. Our goal is to inform you about how to not run into those situations, and how to fix it.

Why A Motorcycle May Only Run On Reserve

If you take a look down near the fuel tank, there will be a dial that is known as the fuel petcock. This petcock allows you to switch between one of three settings. These are “On”, “Off”, and “Reserve”. The “On” setting is the one that you will use most of the time. This uses the main fuel line that sticks up about two inches in the tank. There is a second line that is connected to reserve that only barely sticks up. When switching to reserve, it accesses this other second line. When selecting off, it shuts off flow from both lines.

When riding around, and the fuel drops below the level that the main line can reach, your bike will start to sputter and eventually die. At that point, you can switch to reserve and the bike will drive normally for a short while. You generally have about another gallon of fuel in the tank at this point. It will not get you super far but far enough to get to another gas station and get some fuel.

You may start to notice that your bike only seems to be able to run while on reserve. Even with a full tank, your bike may not start or run while the petcock is switched to the regular on position. There are a couple of different reasons that this might be happening but fortunately none of them are too difficult to fix.

The very first thing that you should check is the screens on the petcock tube. If these get plugged up, they can stop the flow of fuel. As the screen on the reserve tube is separate, you still may be able to get flow through that tube. This would be the exact behavior that we were talking about.

You also will want to make sure that there are not any obstructions or blockages within the petcock itself. Make sure that everything seems clear. Sometimes, even just taking everything apart and putting it back together again is enough to fix this problem. Closely inspect the petcock, the screens, and the tubes and verify that everything appears as it should.

Lastly, there could be an issue with the vacuum on your main fuel line. This could be the result of a hole somewhere in the line or the line becoming disconnected entirely. The main line relies heavily on vacuum suction from the engine in order to flow fuel into the carburetor. Any leaks or breaks in these lines can cause you to lose your vacuum pull entirely.

Is It Bad To Run A Motorcycle On Reserve All The Time?

So, is it actually bad to run your motorcycle in reserve? Could you ride your bike around in reserve all the time? The main reason that you should not do that is for safety-related reasons. Your main fuel line utilizes an engine vacuum in order to pull the fuel into the carburetor.

This vacuum-operated valve is a safety feature. The entire point is to prevent fuel from flowing into the carburetor when the engine is not running. There is no vacuum to pull the fuel because the engine is not running. By using the reserves, you are bypassing this vacuum system. While this is almost never a concern, you must be aware that you have eliminated your protective barrier between you and a flooded carburetor. 

Secondly, if you were to ever run out of gas, you would now be stranded. Your reserve, when used properly, serves as a warning that your fuel level is dropping very low. It is an extremely obvious and loud warning that you need to get gas. By using reserve instead, you are now removing that warning. As long as you keep track of your gas and mileage, this probably will not be a problem. Although, if you are not careful you could end up entirely stranded.

Ultimately, it is not terrible for your bike to constantly run in reserve. There are only two real reasons why you should not, and they are not big deals in the long run. As long as you are aware of how much fuel you have, how far that can take you, and you are sure not to flood the carburetor, it will not matter if you use the reserve. It will not destroy your motorcycle.

How To Fix Motorcycle That Will Only Run On Reserve

So how can you fix a motorcycle that will only run while on reserve? As we mentioned previously, it is not too difficult. Anyone with a small amount of mechanical experience can figure this out. First, you will want to check out the screens. Make sure that they are not plugged up. You do not want anything choking the flow of the fuel, as it is filtered. If you notice anything in there, you can clean it out with compressed air or replace the screens.

Secondly, you will want to inspect the actual fuel lines. Your motorcycle is heavily relying on vacuum suction in order to bring fuel into the carburetor. If there are any leaks at all, you will lose all or some of that suction. This can prevent you from being able to ride your bike with the fuel petcock turned to the on position. If you do notice any leaks or poor connections, you will want to take care of them immediately. Replace the bad hose or make a better seal on the connection and you should notice that your bike is now running properly.

If neither of the aforementioned solutions resolve your issue, there may be some other things to look at. Check the petcock functionality. When you turn it, is it doing what it is should be? Are there any obstructions in the petcock itself? If there are, you need to replace your petcock.

How To Properly Use The Reserve While It Is Functioning Properly

So, what is the proper way to use the reserve setting on your bike? Ideally, you should be using the “on” setting for your everyday riding. This will be the mode that you will use for commuting around town, road trips, and going to the track. The “on” setting offers additional safety features that can help protect you and your motorcycle in case of certain scenarios that we have previously explained. While it is not usually going to cause any problems to ride around while on reserve, it is a simple thing to switch the petcock back to “on” that there is really no reason not to do so.

There are times when you will want to use the reserve. When you are riding in the “on” setting, your bike may start to sputter, or it could die on you entirely. This is the time to turn on the reserve setting. Doing this will allow you to use about another gallon of gas. You will want to ride directly to the nearest gas station from there and get gas as soon as possible. Once you have filled up at the gas station, be sure to switch the petcock back to the “on” setting. 

The reserve setting is only meant for that particular scenario. It is a way to let you know that you are almost out of gas and then allow you to get another 30-80 miles in order to get to a gas station. Anything outside of this scenario should be done using the “on” setting. If your “on” setting does not work for you, we have highlighted several things that you can check in order to get it working once again.

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