1968 340 AVS 4425S carb problems

One possibility since it ran fine in October.
Have you put fresh fuel in since June 1st?
Winter fuel can do that because of its high RVP. When its hot, take the air cleaner lid off and if it gets even worse - its the fuel.

Description suggests lean condition at idle. So it should get a little better when testing as Murray suggests.
If the adjustments don't do anything, then throttles are too far open (unlikely - you haven't changed that) or fuel is not getting through. So at that point check fuel level and passages.