There are two types of gasoline engines: two stroke and four stroke. My favorite is the two-stroke because the amount of power it makes compared to the four-stroke engine. They are also better because they are lighter and have that awesome power band. The biggest differences in these two types of engines are the way they get the air/fuel mixture and when the spark.
Four stroke engines get the fuel and air by opening up valves by the means of a camshaft, cam chain and other valve train parts. These engines are heavy because of all of these extra parts. These moving parts also produce friction, which cuts down on horsepower and adds heat, which also cuts power. Two strokes do not have all of these parts to make friction and extra heat. The piston, when moving up and down, uncovers ports, which are hollowed areas in the cylinder. When the piston moves up, it sucks fuel and air into the crankcase through the intake port and pushes all of the exhaust gasses out of the exhaust port. When the piston starts moving down ward, the mixture is brought up through the transfer ports into the combustion chamber. Once the mixture is brought to the combustion chamber, it is compressed and then ignited by the spark plug, which starts the whole process over again. Because of all of the steps that happen during each move of the piston, the spark plug fires every time the piston reaches the top of its stroke. Two strokes use reeds on the intake port. Reeds are one-way valves that let the air/fuel pass through into the engine, but cannot escape back out. The reason why two strokes are so much more powerful is because of the power band. When driving a bike with a two stroke, one could only describe the power band as flipping a light switch on. When riding on flat ground and the power band kicks in, it WILL be noticed, the front wheel pulls off the ground and the bike gain speed very quickly. To describe what causes the power band is very hard.