Retarding the timing DOES increase low end torque, but only because the cylinder is firing closer to TDC and the burn is starting closer to maximum compression. This robs high end torque because the burn doesn't get a chance to finish before the exhaust stroke starts. Consequently, as RPM increases, it is desirable to advance the spark timing (spark occurs earlier in the cycle).

If you advance the spark to far, the ignition occurs too early, and the momentum of the engine is insufficient to carry the piston through TDC, and will run BACKWARDS. Once the engine starts backwards, now the timing is VERY RETARDED in relation to the engine motion - that is the ignition spark occurs well after the piston goes through TDC, so it won't turn itself around.

I agree that the timing should be checked, and retarded (delayed) by adjusting the Halls sensor. Seems that 23 Degrees BTDC is a favorite value to start with on our airplane engines.

Brad