Rainey began his career racing in the A.M.A. Grand National Championship, a series that encompassed four distinct dirt track disciplines plus road races. In 1981, he finished the Grand National season as the 15th ranked dirt track racer in the country. Following his success in the Novice 250cc roadrace class, Kawasaki hired him to compete in the 1982 AMA Superbike Championship as a teammate to the then defending National Champion Eddie Lawson. The following year, Lawson moved to the Grand Prix circuit and Rainey took over the role of leading rider, earning the 1983 National Championship for Kawasaki.