The balls are usually removed in many race applications since with large cams and high compression piston there is minimual vacume to control the diaphram.The spring is then used for primary control(holding the plates closed) the signal from the manifold and cylinders draw them open.The stronger and quicker the signal the sooner the plates open.With a race engine at high idle or launch rpm or transbrake,two-step luanch or other means of leave negates any effect that vacume has.Just like any sring control on a AVS,Thermoquad controls the flapper wich are under tension the pod spring under compression has the same effect.Vacume tends to only effect mild engines that are footbraked at low rpm and when the engine adverages or exceeds 15inchs at lowrpm.
As far as plates sticking open,this will not happen unless the spring is removed or cut short as to not push the diaphram.Usually when the throttle is released the secondary relaxes to the closed position.To test the diaphram and spring open the throttle by hand and open the secondary,release the secondary and it should retract with the spring.