At light load cruise, you may have more than 34° advance without detonation or ping. Light load cruise has a less dense mixture which burns slower. This requires more lead for economy.
As the throttle is stepped on or opened, the manifold vacuum drops and the vacuum advance drops off. The cylinder density has increased, putting more air and fuel molecules in close proximity for the chemical process known as combustion to take place. This increases the rate of that reaction or burn.
Remember that the intent of tuning centrifugal advance and vacuum advance is to develop maximum cylinder pressure about 10° to 15° ATDC.
From reading the OP, my opinion is the vacuum line is connected to a ported vacuum source. I come by this by the statement that as soon as the throttle is stepped on it starts detonating like a woodpecker on crack. The rest of discussion about weight springs and adjusting the vacuum advance (if it is adjustable) is all a matter of tuning how each reacts.
