More Carb Tuning Questions

Have you tried cranking the timing back?
I tell you what;
if you were to pull off the carb and flip it over, and if you saw almost no transfer slot exposed, then you would know without a doubt that she's running too much idle-timing. Reset the slot to; square to a little taller than wide, using the curb idle screw. After that, do not touch it again. Put it all back together, Start it up,warm it up. Take out idle timing to a minimum of 12*, or until the rpm comes down to 750 ish. If it still won't idle down, NOW, this is almost proof that shes pulling in air somewhere. If you now reset the mixture screws and find them quite far open, that is almost proof that the extra air has no fuel in it, so it is coming from an outside source, or from below the blades. But if you find the mixture screws nearly closed, then the extra air does have fuel in it, and that fuel almost certainly has to be coming from the bowls,lol. So the question then would be where's it coming from. Since the T-Port sync is right, we know it can't be from anywhere but the low-speed circuit.
The first place to look is the fuel level,
then the 4-corner idle system if the carb is so equipped,
then the air bleeds, and finally the PV circuit.
After this if you still have not found it, you will have to blow the thing apart and go look for an internal bypass, engineered or not.
For a stick car, I prefer the DP carb too. I'm a sucker for all barrels blazing at any ol' time!If the tires are spinning too fast,as if, I can always throttle back. I got no patience for vacuum secondaries,lol. By the time they wake up, the urge may have passed.