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.
Scott Ferris died in 1945.
Ferris Greenslet died in 1959.
Sam Ferris died in 1980.
Isaac Ferris died in 1873.
Ferris Foreman died in 1901.
Michael Ferris died in 2000.
Solomon Ferris died in 1860.
Ray Ferris died in 1994-02.
Oscar Ferris Watkins died in 1943.
Frederick Ferris Thompson died in 1899.
Neil Ferris died on 1996-01-30.
Albert Warren Ferris died in 1937.