In 1957, Yamaha released its first 250 cubic centimeter engine, the YD1. The company has had a version of the 250 in every model year since, as of 2015. The two-stroke twin has undergone many makeovers, but remains a fixture in the company's Enduro class motorcycles after nearly 40 years.
The engine became very popular in off road and motocross racing in the mid 1970s. It was first used to power dirt bikes with the IT series motorcycles until 1984. Then it became a main component of the YZ series bikes. Many other manufacturers have stopped making two-stroke engines, but the Yamaha and the Austrian made KTM models remain popular.