Holley stumble trouble

What size is the IFR? I would think it needs to be about 0.038- 0.040", possibly bigger.
Contrary to popular belief, if the IFRs are smaller than above, enlarging them will NOT make the idle richer. If the t/blade position is correct relative to the T-slots, the idle mixture gets adjusted with the mixture screws. Enlarging the IFRs will richen the T slot cct to help with off idle tip in. I am not sure if QF uses a restrictor/restriction to the T slot; often called the IDC, idle down channel, it supplies mixed fuel + air [ volume ] to the T slot. It may also need enlarging, & I would enlarge a minimum of 0.005".
Two other things you could try. A smaller IAB. That will help the idle cct activated higher into the rpm range. A smaller MAB will bring in the mains system sooner to pick up from the idle system tapering off.