If your bike is carbureted rather than fuel-injected, chances are excellent that you'll have a fuel petcock valve with three positions: ON, OFF, and RES. You'll already be familiar with this if you've taken any MSF beginner rider courses, as well as most similar courses from other riding schools.

This valve controls the fuel flow from your gas tank to your engine. If it's not turned on, your engine won't be getting any fuel. As you ride along and your fuel level gets close to empty, the bike will start to hiccup. It's important to know exactly where your fuel valve is and where all three positions are so you can reach down and switch it to RES, short for "Reserve," before the bike shudders to a halt. Ideally, you want to be able to do this without looking, so you don't have to take your eyes off the road. When you do get down this low, you need to find a gas station ASAP. Don't forget to turn the valve back to ON before you ride away from the pump.