Turn the engine to exactly 1/4" BTDC (or 3/16" BTDC for a late-model CSR with a 9.5:1 piston) on the firing stroke

One way to find the right timing position is with a 1/2" socket extension down the plug hole together with a dial gauge. Or you can just mark off a suitable peg in the plug hole.

Without turning the engine, make sure the rotor fixing bolt is loose and rotate the rotor until a white timing dot appears exactly under the hole that is clockwise from the pickup coil

Tighten the rotor bolt, making sure the crank doesn't move. The timing is now set.