1st off, love the car. 2nd, i have no first hand knowledge of how a blow thru carb operates, so i'm just spit ballin' here.
When i saw that you played with the 4 corner idle and saw some temporary results it had me thinking it may have been acting rich? If so, is there a chance your fuel pressure has increased for some reason. Maybe a faulty regulator if your using one?
No, I’ve got a fuel pressure gauge on the cowl and an air fuel gauge. Pressure is normal and air fuel ratios are in line. Thanks for all the ideas though. This is what I was looking for.