The two-stroke cycle of an internal combustion engine differs from the more common four-stroke cycle by having only two strokes (linear movements of the piston) instead of four, although the same four operations (intake, compression, power, exhaust) still occur. Thus, there is a power stroke per piston for every engine revolution, instead of every second revolution. Two stroke engines can be arranged to start and run in either direction. The smallest gasoline engines are usually two-strokes. They are commonly used in outboard motors, high-performance, small-capacity motorcycles, mopeds, scooters, snowmobiles, go-karts, model airplanes and motorized garden appliances like chainsaws, edgers and lawnmowers. In each application, they are popular because of their simple design (and consequent low cost) and very high power-to-weight ratios (because the engine has twice as many combustions per second as a four stroke engine revolving at the same speed). For handheld devices, they also have the advantage of working in any orientation, as there is no oil reservoir dependent upon gravity.
Two-Stroke Gas Scooters
Most modern scooters are two-stroke gas scooters, for this simple reason: there is more bang for the buck. Two-stroke gas scooters, because of their high power-to-weight ratio, are faster than four-stroke scooters.
In the past, two-stroke scooters used premixed fuel, combining gas and oil together, similar to a lawnmower. Today, many high end motor scooters, such as a Vespa or any GS MotorWorks two-stroke scooter models, have an auto-lube system which automatically injects oil into the gas tank, thereby eliminating the need to premix.
Yamaha Gas Scooter Engines
Yamaha just celebrated their 50th year of operations. They make some of the best engines, both two-stroke and four-stroke, for gas scooters. In addition to their own Yamaha gas scooter models, Yamaha makes engines that other manufacturers use in their gas scooters. Yamaha mopeds range in size from 49ccs, like the Yamaha Vino, to the 249cc Yamaha Morphous. Yamaha scooters, particularly the Yamaha Vino, is similar in style to the GS MotorWorks Retro and Retro XL gas scooters. In fact, GS MotorWorks in the past has used genuine Linhai Yamaha engines in some scooter models, including the Euro, EuroElite and Retro scooters. Yamaha motor scooters are expensive, ranging in price from $1,849 to $5,199. A top end Morphous Yamaha gas scooter costs about as much as an entry-level Harley-Davidson motorcycle. Dealers sometimes refer to these Yamaha mopeds as Yamaha Scooter Motorcycles, because of their size, displacement and price.
Linhai-Yamaha engines and Linhai-Yamaha mopeds are manufactured by Jiangsu Linhai Yamaha Motor Corporation, a Chinese company, under license by Yamaha Motor Company, Ltd. Linhai-Yamaha is a partnership of Yamaha motor scooters.