Does my scooter have a two-stroke or four-stroke engine?
Two-stroke engines are used in most all 50cc Japanese scooters, though some manufacturers are starting to use four-stroke engines. They are also used in the Honda Aero NH80, Aero NH125, and a handful of Japanese scooters overseas. Here in the U.S., virtually all we see are the 50cc two-strokes. For a good explanation of how a two-stroke engine works, see:
Basically, a two-stroke engine completes a combustion cycle in two strokes of the piston - up and down. A four -stroke engine requires a up-down-up-down movement of the piston (which is 4 strokes of the piston). The advantages of two-strokes is that they are lighter, simpler, easier to work on, have fewer parts, and are less expensive to manufacture. They also have the potential to pack about twice the power into the same space because there are twice as many power strokes per revolution. The combination gives two-stroke engines a great power-to-weight ratio.
But two-stokes do have some disadvantages also:
New technology using computerized fuel injection has mitigated that last two disadvantages, but it's unlikely that we will see this technology used in scooters any time soon. For the most part, a lot more money is spent on four-stroke technology, so it is much further advanced.
Four-stroke engines are much more common in the U.S. than two-strokes. They are used in the Honda Elite CH80, CH125, CH150, and CH250. Yamaha uses them in the CV80, and Riva XC125, XC180, and XC200.
For an explanation of four-stroke engines, see: