How old were the 2 mechanics ?, they may(due to age) have no experience with carbs, as this is a easy fix with more detail or the car in front of you.
It sounds very much like the car, or at least a fuelling fault, which can be caused by things other than the carb.
You could put a new carb on and have exactly the same problem still along with the new one, a empty wallet!!
These really are the most basic carbs going.
Running rough ?, does it idle at the correct speed, either hot or cold, is it different when hot or cold symptom wise ?
It could be something as silly as the idle speed needs raising, a vacuum(inlet) leak, even a weak fuel pump can cause this, but be ok when accelerating as there is more pressure from a faster running engine.
The idle speed should be 750-850rpm(hot), and cold on choke 2600-2800rpm.
There are 3 diaphragms in this carb, 2 of which will defo cause what you have, but need more info, especially is it the same hot and cold, there is also a anti dieseling valve fitted to most of these, it could just need richening up, more detail needed.
It's an excellent carb if in good order ace on fuel and good power so worth fixing.
Does the exhaust smell rich, what colour are the plugs, should be light/ish brown.
tabetha