Duncan called Lansdale, PA home. His racing career spanned seven decades from 1928 through the 1980's. He raced Midgets, Sprint Cars, TQs & at the Indy 500.

In the 50's the AAA joined with ARDC. Duncan was the AAA Eastern Midget Champion in 1953, 1954 & 1955. From 1955 until 1967 he won eight ARDC titles.

During WWII, Duncan was assigned as President Truman's driver during one of his visits to England.

The great Mario Andretti credits Duncan with having a great influence on his professional life.