The incident happened on a stretch of the course between Cooley Hill Corner and Castle Corner.
The crash happened during the fourth lap of the Junior Support Race - the second race of the day.
Mr Murphy was from Lusk in Co Dublin.
It is the second road racing tragedy to hit that village in recent years. In 2008 Martin Finnegan, also from Lusk, died in the Tandragee 100.
Tragic. Formula One has become reasonably safe in recent years, but Motorcycle Road Racing continues to be very dangerous.