Hi Richard,
The technique of setting the ignition timing in the original manual is a little bit obtuse, and requires that the engine is exactly as it left the factory. It doesn't allow for wear, or bastardry, that may have occurred over the life of the bike.
You can very easily check the timing on an outside-flywheel motor. Set the magneto to full advance and remove a spark plug. Move the engine by hand until the piston it exactly at TDC on the firing stroke. Mark the flywheel with a marking pen. Using a flexible tape (a dress maker's tape is ideal), measure the circumference of the flywheel, then make a mark on the flywheel at one tenth of this distance before the TDC mark. (One tenth of one revolution is 36 degrees.) Rotate the engine to this mark. If the timing is correct the points should be just opening.
From your description you may be running with the timing a bit retarded. One tooth change will probably make it over advanced.
Retarding the ignition should help when the motor is in "slog" mode before the snatch is made for first on a long hill. By this time the air lever would usually be closed a little also.
By the way, if you slowly pull the rear wheel of a TS you should feel strong compression for each cylinder, to the point where the belt my begin to slip a bit before the compression is overcome.
I suppose there are 1920s TSs that romp up Sunrising?
Cheers
Leon