carbed out

Ok , how's this sound; when you had the idle timing set to 15*; the all in was 34*. Is that right? If yes, then there is 34 - 15 = 19 in the dizzy. Typically the dizzy-cam will allow 20*, so you read it nearly right on.
This also means that whatever you set the initial to, the all in will always be 19/20* more. So with 12 initial, the all in will be 12 + 20 = 32. The 2800 does not change.
So far so good?
I suspect the Vcan diaphragm is ruptured.That means, as soon as you crack the throttle, the carb will suck air through the diaphragm and make trouble. Check it out. If I'm right, plug the line into the carb to prevent that.Then as time permits go get a new can.
I also feel that the timing may be coming in too fast, for your combo.I think your timing experiments are proving that. I assume these tests were not done in N/P, but on a loaded engine while driving?