If your motor scooter has been sputtering and dying while running at idle speed, or if it is roaring at too high of an engine speed while you're stopped, you may need to adjust the idle speed. This is done by turning the idle screw, a simple flat or Phillips head screw near inside the engine compartment. The only difficult part of adjusting your idle screw is finding it in the first place.
Refer to the owner's manual for your scooter and look up the location of the idle screw, as its specific location varies from one model of motor scooter to the other. Typically, the idle screw is attached to the carburettor compartment, near the choke. This is often on top of the engine block.
Find the idle screw on your motor scooter and expose it so that it is easily accessible. This will almost always involve removal of the engine compartment cover, which does not require any special tools on most modern scooter models. With the engine exposed, the idle screw should be in plain sight.
Turn on the scooter. If the idle speed is set so low that the scooter sputters and dies before it can start and stay running, turn the idle screw a quarter turn or half turn to the right before you can start it.
Adjust the idle screw while the engine is running. Turn the screw to the right makes the engine idle faster, or to the left to make it idle slower. The screw should only be turned a quarter turn at a time to prevent engine damage. After each quarter turn, wait at least two minutes before adjusting it again. Observe any changes in engine RPMs on the tachometer, if your scooter has one.
Turn off the scooter and replace the engine compartment cover once you've set the idle speed where you want it.
Changing the idle speed may work as a short-term solution for a scooter with an engine problem, but it is not a substitute for repairs. An engine set to a higher idle speed will burn more gas than one set to a lower idle speed.