A two stroke engine is usually smaller but has more power. It has one power stroke for each revolution of the crankshaft. With a two stroke bike, they are built more for racing and less for long distance riding. If you ride a two stroke for a longer distance it will blow up easier. In a race a two stroke will most likely win in the beginning but overall the four stroke will be faster. Two stroke gas isn't just plain gas like a four stroke. It has to be made special with oil.