Common problems with gas scooters usually involve the battery and carburetor. A scooter that doesn't start all of a sudden is likely due to a dead battery. Another common issue is a faulty fuel gauge. Look inside the fuel tank to make sure there is sufficient gas present.
Batteries lose their ability to hold a charge over time and need to be replaced. Carburetor issues occur slowly over a lengthy amount of time. Carburetors that go out of adjustment prevent scooters from starting and accelerating smoothly. Gummy deposits accumulate inside carburetors over time and can prevent it from working optimally.