As i said earlier, your item looked like a choke breaker to me, and all my old khyber books are buried/lost in my pile of tools and books in storage.
But its easy to check, the choke breaker should slowly pull and hold the choke plate open as the engine starts up, if its sudden then the little vacuum bleed is not working.
The dashpot works by accelerating the engine and leaving suddenly. You will see the dashpot pulled in while engine idles and then as you pull the accelerator it should extend and when you leave the accelerator it will hold the throttle open for a bit of time before slowly retracting fully and allowing engine to idle normally.. You can get the dashpot slow bleed if you look for it in market, (most probably will find an old part). The picture and explanation and replacements were posted above. Aisan and Toyota parts are the same just different colour, you can also use keihin/Honda part and also hitachi/nissan/mazda part - they are similar to aisan part, just smaller in size.
Didnt your carby guy check that all parts of the carburettor are working?
Please link the thread here where you copied the pictures from.