750 qf vac sec running rich

#1 Primary throttles open too far at idle.
#2 Fuel levels set too high (Check this first as you standard oeprating procedure any new or worked on carb)

Generally less throttle is needed at idle when more initial timing advance is used. Say its set at 10* BTC at 1000 rpm. In which case adjust it for 14* to 16* BTC at 1000 rpm. Then after its warmed up, reduce the speed with the throttle stop screw. Say to 800 rpm and recheck the timing. It may have dropped back a couple degrees.
That done, readjust fine mix screws. There should be response to changes - especially when closing them off (too lean is always more obvious than too rich).

Repeat as required. Test driving (low speed and steady only -NO wide open throttle) to confirm results in gear.

Another way to do all this is take the carb off, observe the primary side transition slot openings and make sure only .020 to .035 shows beneath the bleadees when shut. Holley says .040 but QF t-slots may be wider or longer than old school Holleys.

#3 Modify the carb. This is more involved and does not change the procedure above. Relocate the idle feed restriction so its always submerged and get rid of excess e-bleeds. This simply will make the way the fluid moves more consistant.