If the mixture screws have little or no effect it is likely because you have advanced the throttle plate past the first progression hole.. There are three different types of Weber needle valves and they should not be changed to the non original type. Gordon Raymond knows the details. The correct needles are usually about 4 turns out from fully closed.
Your symptoms could be retarded ignition so check that. Also be aware that your emissions carbs require type 2 idle jets, say 55F17, 50F21, etc. F8, F9, F11 will not work properly in these carbs. Also the emulsion tubes should be F34 or F41. F9, F16 etc will not work properly.
I had to increase the idle screw a lot to get the engine rpm up to around 900/1000rpm which most probably placed the throttle plate past the first progression hole. With the idle screw not in contact with the arm, the throttle plates are exactly covering the top (closest to engine) progression hole. Is this OK ? As the slightest adjustment, will start opening up the first progression hole.
The new needle valves were supplied with the rebuild kit I got and since I saw them stamped with the same number as the old ones, I change them to the new ones. I still have them which I can swap. Also note that I did not have the washers before as I described in my first post. Is this OK ?
I have adjusted ignition the best I could with the rough idling at around 1000rpm. I will recheck the lighting gun is triggering on the F mark on the pulley.
All other jets, tubes etc. are all original and used the ones fitted when engine was running fine.
1971 - 2000 GT Veloce Euro