[tdz840]

I cant comment on this particilar weber but the principals are the same for all.
I have a set of Solex ADDHE which are similar to the DCOE which again is similar in principal to your carb.
Everything appears to point to fueling
Assuming the ignition is spot on (use the basic B20 specs is a good startng point). You wont tune any carb if the ignition specs are not correct
Spark plugs - what colour
Idle screw. 1.5 turns out - if more than 2 then idle jet is too lean if less than 1 then too rich. Change out in tranches of ten
Idle jet - typically should correlate to the choke size i dont have the calc to hand
Main jet - again correlates to the choke size change in tranches of 5
Air Corrector- minimal effect below 3500 as most of the air is coming via the emulsion and idles (idle jet is a mixture of fuel and air)
Finally emulsifier - these are rarely changed and if the car has been running right on this engine i would suggest to leave well alone. If it has never run right then you need to check that. I may have some baseline specs somewhere
One point re the progression holes.
If they are uncovered with the throttle plates on the stops then you are masking the problem. In effect you are adding fuel when it shouldnt be added. The ‘system’ should be soley on idles up to 1500. If the progressions are uncovered below that then its supplementing the idles. The progressions only fill the ‘hole’ between idles and mains.
Russ