I have/had the same pull through . From reading it appears as not unusual . As it only happens at high rpm/throttle/load just jet as needed be secondaries for best afr .

Tex

New best ET 10.259@129.65 .
New best MPH 130.32
Finally fitted a solid cam,
stepped it up a bit more
3690lbs through the mufflers
New World block 3780lbs 10.278@130.80 . Wowser 10.253@130.24 footbraking from 1500rpm
Power by Tex's Automotive