Modern distributors have two advances, not included are computers. The vacumm advance which most everyone recognizes by the diaphragm pod on the side of the dizzy with the vacumm line attached. A centrifugal advance which usually consists of a set of springs and weights. In the case of your distributor the mechanism is under the point plate. The factory HEI has the centrifugal advance under the rotor. In any case the vacuum at max holds the distributor advanced per a degree of advance set by the diaphragm. When you open the throttle and the vacuum goes to to minimum the centrifugal advance takes over. The centrifugal then advances the distributor at a rate determined by the springs and weights. To recurve the distributor is to change that rate. Why recurve, better performance.
Larry
68 C20 327 daily driver
63 C20 292 Camper truck
65 C10 ? Custom Cab AC,PB,PS,$flasher
