This really helped me when I was learning the SUs. Thank you @240260280

https://www.classiczcars.com/forums/topic/39221-quick-and-dirty-su-tuning/

So, as I ponder a possible carb conversion I wanted to begin by educating myself. This guy on YouTube seems to really know about these SU carbs. It might help all interested parties get those carbs tuned right. This video is part 1 of his SU tuning series.

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Before you rip them out and replace with different carbs... you can do a small rebuild yourself.  If that isn't in the cards, just send them over to Ztherapy for a rebuild.

I think you should find a good rebuild able set, buy the kit from ztherapy.com that comes with the DVD for general instructions. I love videos but the only way for me was the hands on approach. You clean them as you go, make sure and keep the parts separate to the front and rear, wipe them down with this stuff and you'll be happy. BTW, how deep have you already gone with the EFI? That's something to consider in my opinion. That's why I have a set of SUs mounted on the wall in my garage. I replaced my whole EFI system before I bought a 240 and fell in love with the carbs. I'm sure you seen this but I'll post it again.

Basically constant vacuum carbs are very easy, but if you are used to downdraft carbs like most US cars use, it can be confusing at first.

The screw on the lower part is mixture control. The vacuum controls the fuel delivery. The choke pulls the venturi down ( same like putting the needle up ) and creates a richer mixture. Float bowl level has to be right offcourse and all the parts function correctly. Carbs can be synched by hand and view ( watch throttle valve opening ), but with an air flow synch tool is better and more accurate.