A minibike, also recently known as a mini moto or pocketbike, is a miniature motorcycle. Most traitional minibikes use four stroke engine to turn the rear wheel via a chain. Small cheap gasoline engines like ones produced for yard equipment are most often used, though most designs require a horizontal crankshaft engine. This means that typical walk behind mowers, which use vertical crank engines, cannot be used. Some models use a two stroke engine, and electric-powered models are also available. A 2-stroke engine usually creates a louder, higher frequency noise then a typical four-stroke engine, this is do to the fact that a two-stroke engine has a power power stroke, and subsequent exhaust pulse every rotation of the crankshaft, while a four-stroke has a power stroke, and an exhaust pulse every other rotation of the crankshaft. In effect, two-strokes sound as if they are operating at double the speed of a four-stroke engine. Also, an improperly tuned two-stroke often releases unburnt fuel, and thick blue smoke out exhaust during normal operation, these features, along with a minibike's small size, mean that minibikes are rarely street-legal.