That bed sheet at the back looks exactly like mine.....oh wait a minute this is my pic as well..
This is not knocking......i experience the same things at high speeds....2-3 secs hesitation...when throttle is closed and reopened at high speed......after getting everything checked i think it has something to do with timing....but since it only occurs at high speed and very slightly so i have left it as it is.....it's been an year now since head work....so don't worry about it...
Btw: I have installed Euro 2 carb on my non euro as well....
Plus you talking about removing the Euro 2 system......it can be removed but you have to change the insulator or intake manifold as well....cuz there is a pipe coming from ASV valve to the insulator and when the ASV system would be removed plugging that hole in the insulator is not good enough as it needs to be air tight.
So you would need to attach old model insulator as well....one which doesn't have opening for pipe...