Springs only control the rate of advance- - - -the distance the weights travel control how much advance there can be. Every degree of advance at the distributor cam translates to two crankshaft degrees, since the camshaft and distributor turn at half crankshaft speed. 15 degrees of distributor cam rotation would translate to 30 crankshaft degrees. Most engines (even modern V8s) run best with around 36 or 37 degrees of centrifugal advance at the crankshaft, with about another 10 added when the vacuum advance is maxed out. That vacuum advance goes away almost instantly when a load is applied to the engine, such as hill climbing, passing, or pulling a trailer.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!