Clip a small light across the DYNA. It will turn on as you inch past the timing point. I use a spare instrument light with crocodile clips on the leads. IIRC one goes to the coil connection (DYNA side not battery side) and the other lead goes to ground. Turn the motor over slowly with a wrench while you watch the timing marks with all four plugs OUT and grounded to the motor.
The light should go on at the exact F marks. If not, adjust. Then repeat while with your other spare hand you keep the rotor rotated against the springs. It should now come on as it passes the full advanced marks.
When that's all in order, replace the plugs and check timing with a good strobe. Test to see that it moves from F to full advanced smoothly on each and every plug lead. Any that show odd results or interruptions, need investigating.
The light should go on at the exact F marks. If not, adjust. Then repeat while with your other spare hand you keep the rotor rotated against the springs. It should now come on as it passes the full advanced marks.
When that's all in order, replace the plugs and check timing with a good strobe. Test to see that it moves from F to full advanced smoothly on each and every plug lead. Any that show odd results or interruptions, need investigating.