Advance past 28 or 30 past BTDC is no help at all with rpm....The advance is set for 28 with the throttle plate exactly parallel to the throttle bore...If over rotating the carb makes more rpm the advance was not set right in the first place...
An engine with syncro spark will show that over rotating the carb will NOT gain rpm, the advance is fixed at 28 or 30 no matter what the throttle position is ...Over rotate it far enough and the engine will slow down....