Youmans was born in Tampa, Florida, and was a childhood friend and Hillsborough High School teammate of former Mets pitcher Dwight Gooden before moving with his family to Fontana, California.

After splitting the 1984 season between the Lynchburg and Jackson Mets, Youmans was traded on December 10, to the Montreal Expos along with Hubie Brooks, Mike Fitzgerald and Herm Winningham for future Hall of Fame catcher Gary Carter.

After the 1987 season, Youmans checked into an alcohol rehabilitation center under speculation that he had been forced to do so by Commissioner Peter Ueberroth.

[9] Youmans was 3-6 with a 3.21 ERA when his 1988 season was cut short on June 25 by an indefinite suspension for "failing to comply with his drug-testing program.

Youmans pitched for the independent Sullivan Mountain Lions and Newburgh Night Hawks of the Northeast League in 1995, and became a coach for the Catskill Cougars the following season.