This tutorial will work on Honda CB450's 68-74 and Honda CB500t's 75-76.

Ignition Timing -

Before attempting to adjust ignition timing, make sure the contact breaker point gap is adjusted properly.

1. Connect the timing light to the system for the left hand cylinder properly. 

2. Start the engine and allow it to idle at 1,100rpm

3. Aim the index mark with the timing light and see if the LF aligns with the index mark. If not aligned, loosen the screws and manually rotate the base plate in either direction. Rotating the plate clockwise will advance timing and counter clockwise will retard timing.

4. Connect the timing light to the ignition system for the right hand cylinder.

5. Restart the engine allow it to idle at 1,100rpm.

6. Aim the light at the index mark this time it should align with the F mark.

If you cannot get it so that LF and F are on the index mark. Either your points gap is incorrect or you need to replace the contact breaker point assembly