Weld won the 1963 Knoxville Nationals, the premiere event in sprint car racing. Weld raced in the USAC Championship Car series in the 1965–1972 seasons, with 36 career starts, including the 1970 Indianapolis 500. He finished in the top ten 11 times, with his best finish in 4th position in 1970 at Sacramento. He was also the 1967 USAC Sprint Car Series champion. He was the last driver to pilot a car powered by the famous Novi engine at the Indianapolis Motor Speedway when he crashed during a qualification attempt in 1966.