Rory Harley Davidson, 23, was travelling with another man on the bike on Monday morning when it struck a stone dyke in Boig Road, New Cumnock, near to Nith Bridge, causing the pair to be thrown off the vehicle.
The second man was taken to Ayr Hospital, where staff described his condition as critical.
Mr Davidson, who was from New Cumnock, died at the scene of the accident.
Police are continuing to investigate the crash and have appealed for any witnesses or drivers using dashcams in the area to contact them.
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