Most common problem is the seat switch. The machine must detect the presence of the operator in the seat to prevent the safety circuits from killing the engine. If it is a commercial walkbehind mower, then it would be the bail(s) attached to the handles and the switch associated with those.
Ferris Greenslet died in 1959.
Michael Ferris died in 2000.
Isaac Ferris died in 1873.
Scott Ferris died in 1945.
Solomon Ferris died in 1860.
Ferris Foreman died in 1901.
Sam Ferris died in 1980.
Ray Ferris died in 1994-02.
Albert Warren Ferris died in 1937.
Sarge Ferris died on 1989-03-12.
Oscar Ferris Watkins died in 1943.
Pervis Ferris Young died in 2003.