The Importance of Turning off the Fuel Valve on a Motorcycle
When you go to start a motorcycle, there are 3 things you usually have to do before you push the start button or kick start if. Turn the key to the "on position", switch the engine to "run" (usually located on the right side of handle bars so you can hit it with your thumb) and reach down and switch the fuel valve to on. The valve can be located on either side of the bike and will have 3 selections. ON, OFF, and Reserve. You will need to put turn it to the "On" position.
This valve is what allows the gasoline to leave the tank and go into the carburetors (or fuel injection system on a newer bike). It isn't anything high tech. Gravity makes the fuel leave the tank through a fuel line, passes through this valve and eventually into the engine.
Many people (especially seasoned riders) tend to skip 2 of the 3 steps. When they are done riding, they will turn the bike off and take out the key. They will leave the engine switch on run and the fuel valve in the on position. In defense of that line of thinking, most people have gotten really angry when the motorcycle won't start and finally figure out that the engine switch was off or the fuel valve was in the off position (essentially making the bike out of gas, even with a full tank)
This author has been guilty of that on several occasions. Leaving the engine switch in the on position can pose problems as well but that is another article. What we are concerned with is the fuel valve.
People will be tempted to ride the bike in the reserve position as well. The problem with that is when/if you run out of gas, you have no back up. The reserve tank isn't really a separate tank. It is a lower portion of the gas tank. Reserve is an option so that if you run out of gas, you have 10-15 more miles (that number varies from bike to bike, tank to tank, and riding style) to get to a gas station. If you have been running the entire time in the reserve position, when the motorcycle sputters and dies from fuel starvation, there isn't that little bit left to get you where you need to go to fill the tank up.
As stated earlier, many people will leave the fuel valve in the on position. While this may seem like a harmless thing to do, it can have consequences. While it is turned to the on (or reserve) position, the valve is opened. In effect, you have taken a check valve out of the system.
Since (mostly older motorcycles) work on a gravity feed, the fuel will run out of the tank. If you have left the valve in the open position, the fuel goes straight through it and into the carburetors. Why is this a problem? The best case scenario is that you have flooded out the carburetors. While this can be a pain in itself, more damage can be done.
For anybody that has ever had to rebuild a carburetor, you know that there is just under a million little pieces. Needle valves, diaphragms, gaskets and a plethora of screws. The wonderful thing about carburetors is that not only does each type of bike (Harley Davidson, Yamaha, Honda etc) have there own designs, each model and even year may have different ones on them. This is why even DIY people will usually take a carburetor to a professional to have it rebuilt. One small mistake and it is nothing but a paper weight.
The complicated aspects is the corner stone of why it is important to always turn it to the off position. Gasoline is a corrosive liquid. Any bike owner that has spilled fuel on their tank at a gas station knows all too well how easily it can ruin the finish on a paint job. This particular property will wreck havoc on the rubber and plastic parts of the carburetor.
When the motorcycle is running, the fuel passes though the carburetor and into the engine. If the motor isn't running, the stopping point for the fuel is the carburetor. As it sits there overnight, it is doing damage to all of the parts that it touches. This can lead to having to rebuild and replace parts on the carburetor (and some of the littlest parts are the hardest to find and most expensive).
As far as newer bikes are concerned, the same basic principle applies but the damage will be done to the fuel injectors.
Another part of the motorcycle that can be damaged is the fuel line. This isn't that big of a deal. First, the line is made to have gasoline in it so the damage is minimal but over time it will break down the rubber. If you have steel lines (which are rare) it can still be corrosive to them. Second, there is still a fuel line from the tank to the valve. Even if the valve is turned off, there will still always be gasoline in that part of the line. In this situation, the fuel lines are the least of the concerns.
As the gasoline eats away at gaskets and other non metal parts of the carburetor, complete break down isn't the only thing that can happen. You may just get a leak on a gasket. This can cause the engine to run incorrectly because of the fuel-air mixture and it can also (if large enough) be a leak in fuel system.
If you have a fuel leak you may find that you are running out of gas sooner than you think (many bikes don't have fuel gauges so fill ups are based on the odometer). While that is definitely a problem, an actual danger does exist. Dropping a highly flammable liquid on a super hot engine can lead to problems. Imitating the Ghost Rider going down the road in a ball of fire is not a cool way to travel.
All of these problems can be solved by simply reaching down and moving the switch to the horizontal position (on and reserve are both with the switch vertical). The amount of time that is saved by leaving the fuel valve "on" definitely does not out weigh the risks and damage it can do to the bike.
