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Yamaha and Doug Henry get most of the credit for the development of the modern four-stroke, but there’s so much more to the story. As the last century
Source: FORGOTTEN FOUR-STROKES THAT SPARKED A REVOLUTION | Dirt Bike Magazine

The Dirt Bike Academy offers adventure bike and dirt bike training classes for both complete beginners and experienced riders in Pennsylvania’s Pocono Mountains. We teach kids and adults in separate classes for dirt bike riders and adventure bike riders. Our beginner coaches and classes are fully certified by the Motorcycle Safety Foundation.