tune is one thing.
there is also the possibility there is a error in the rebuild.
It could be a rebuild error what is causing the increase in RPM. Perhaps being intermittent, its a little harder to identify.
The DCOE 72/73 are emissions carbs so you may well need more than two turns out on mixture screws. My limited experience with the emissions carbs says opening the mixture screws four to five turns is within the norm.
Regarding the high idle, an air leak comes to mind. Do you have the proper carburetor support in place? A sticky advance mechanism in the distributor could delay a return to idle.
My plan is to try with more turns on the next try. I am not sure what are emission carbs are but the carbs are original to the car and it was sold for the Italian market.
I really doubt I have an air leak as this is very intermittent and not constant. I do have a support bracket.
Can an electronic Pertronix Ignition system inside the distributor stick in advance too ?
Maybe not related and checked already but i had the same issue of random increase rpm after i did a rebuild of my DCOE 106/107, mine turned out to be throttle linkage/cable issues (sticky and catching). When in the engine bay working throttle by hand i had no issues but using peddle different story. If yours is LHD then hopefully linkage & cable will be OK, my 1600 spider had a poor RHD conversion hence the issues.
When the RPM's went up in front of my eyes, I immediately checked the linkages and all were home.
1971 - 2000 GT Veloce Euro