Quick guide with pictures on how to change the idle speed on a motorcycle and why you might need to.
Idle speed is the rotational speed of the engine when decoupled from the drivetrain without any throttling being applied. This information is displayed on the rev counter next to the speedometer on both cars and motorcycles. The rev counter shows how many times the engine's crankshaft makes a full rotation in a minute. The common term for it is RPM (revolutions per minute).
Idle speed must be adjusted when too low (the engine will keep stalling) or too high (causes engine wear and shortens its lifetime). Idle speed of a warmed up motorcycle engine should be between 1000 and 1500 rpm.
Wait for the engine to reach its normal operating temperature and do not adjust the idle speed while the choke is on as it gives inaccurate reading. Refer to the motorcycle's manual, in this example the adjusment is made on a Suzuki SV650S, where the idle speed control is located on the left hand side below the tank. It is easily accessible and requires a phillips screwdriver only: rotate anticlockwise slowly to decrease or clockwise to increase idle rotational speed of the engine while observing the rev counter. Older motorcycles may require slightly higher rpms to prevent stalling while idle, but do no set it over 1500. That can indicate other problems that need to be looked at and repaired.
Most modern motorcycles come with automatic chokes, which increase the RPM after igniting a cold engine to reach operating temperature quicker and prevent stalling. Manual chokes on bikes can be on the handlebar (which allows to start riding) or at the side around knee-height that makes it impossible (or very dangerous) to turn it off while riding. The choke shouldn't be used in warm weather or left on too long in the cold (usually a few minutes is enough) as it causes unnecessary engine wear. Normal operating temperature of a motorcycle engine ranges between 70 and 105 Celsius.