The main problem with membrane carbs on single cylinder engines (or opposed twins) is that the carb membrane admits a little bit of fuel EACH stroke. The main needle opens and closes,bounces on the seat, and the fuel admission rithm may get out of tune with the engine rpm. This can only be solved with a large plenum chamber, which however opens up a new can of worms.
Another problem to address is the idle transition mixture control. Walbro type carbs (walbro, tillotson, bing, dell'orto etc) have a strange way of brake air mixing into the fuel flow. At one time the second or third idle jet acts as brake air jet, the other time it acts as idle jet. This makes tuning a membrane carb very difficult.
In float carbs there were well defined and well separated items like slide chamfer, slide needle, main jet, air jet and float height to play with. Still quite a few variables, but a mechanic savvy to his engine would have the tools in his box to tune the carb for the day, morning or evening. If I play with the seemingly simpler walbro, it often gives me fits, because one change influences almost the whole adjustment range. No wonder there are so many Walbro numbers available, without any system in the numbering.
Some folks at Walbro seem to know what they are doing, but the best they can do is make a new setup for a new engine. Or so it seems.

Edit:
Grammar.