From how stuff works:-
2 Stroke Engines
http://science.howstuffworks.com/two-stroke.htm
4 stroke engines
http://science.howstuffworks.com/engine.htm
Once u read the above 2, u wiill know why, 4 strokes engines are
generally more quiet and cleaner. The only advantage of 2 stroke
engines in Singapore, is because of power. A 2B 2-stroke engine,
SP, RXK,RXZ, Phatom 150,etc are generally more powerful than their
2B 4 stroke engine.