Timing Mark not showing up??

Is the damper marked beyond 10 or 12 degrees?
The timing could be advancing at 800 rpm so at 900 rpm its at 15 BTDC and at 1000 it could be 18*

Another possibility is the lighting in the engine bay versus the light emitted from the timing light. Some of the older ones don't have a strong light source. Can you see the flashes?