Anybody have experience with Demons. 750 double pumper’s that is.

I have used two of the Holley Demons [ black plastic centre ]. One a 625 on a Chebby, worked ok. Other was a 750 on a 400 Pontiac, could never eradicate the bog when the secs opened. Owner rang Holley, tried all the 'fixes'. Original QJ went back on, no bog.