BSA did not print a manual for your bike but rather separate service sheets to cover various jobs that they deemed suitable for the home mechanic capable of doing.
Haycraft rearranged them into a book form called "the book of the BSA twin" published by Pitman press.
You can get complete sets of these on CD from almost anywhere.
For day to day stuff like lubeing & adjusting the carb, etc you need to get a copy of the rides handbook also available on cd from almost every where
