Open to all riders from the year of their 6th birthday, to 31 December of the year in which their 15th birthday occurs. Limited to 4.0 hp air-cooled engines. Any production reeds, air box, clutch, wheels, tires (with or without pattern). Brake levers may be switched from their factory fitted side, but front and rear brakes must operate independently of each other and no single lever may control more than one brake disk. The use of hydraulic brakes is prohibited.