Weber had many features for emissions carbs. Some carbs had all of the features but others only had a partial set.back to topic, my understanding is that with EmCon carbs you can not interchage E.Tubes like in the older ones, it doesnt work that way, like the tube has a lot more and bigger holes for the transition phase, older ones doesnt have this feature, stick with the original ones and play with the fuel and the air
These features include:
Feeding the progression circuit from the well rather than the float bowl.
These required different emulsion tubes, usually F34 or F41 which are interchangeable.
They also required type 2 idle jets, typicaly F21 or F17
4 or 5 small progression holes rather than 2 or 3 larger holes.
Idle mixture screws with a narrower taper, more than one design
Air balance screws around the throttle plates.
Larger auxillary venturis which extend the progression range and bring in the main jet at higher rpm.
Many emissions carbs required larger main jets than classic carbs with the same venturi size.
The carbs in question here are 40DCOE44/45. They have "classic" progression plumbing and use "classic" emulsion tubes and idle jets.
At part throttle up to about 3000 rpm, idle jets have the most influence.
At part throttle and higher rpm main jets have the most influence.
At WOT main jets and air correctors have the most influence.
Certain emulsion tubes work best with certain cars. 4 cylinder Alfas always had either F9 or F16 unless they were emissions carbs. I have experimented with F9 and F16 with data logging. F9's are marginal at high power and rpm and tend to run lean. To correct that you have to install bigger main jets and that makes the mid range too rich.
A float level that is too low will cause leanness, particularly in the transition phase. One that is too high will cause richness .