Not enough screw to adjust advanced timing (static)

Finishing final steps of tune up with static timing check until I can find my timing light or get another. Retard and pick up timing need no adjustment. However, when adjusting full advance timing, I am a long way from being able to align the mark on the flywheel to the mark on the magneto plate. Need 15 - 20 mm more on screw.Does this mean something else wrong? Can I replace the adjustment screw with a longer one in order to make the adjustment? What's the danger of running this motor without the full advance timing set correctly? I never run at WOT.

Forgot to include: 86 150 ETL