Conrad,
I can't see how the servo would be a problem on acceleration as the vacuum release should have been done, the main CV check valve closed, and the reducer valve in the CV should be shut. Theoretically possible to have the CV diaphragm providing a huge leakage, but then you'd have shifting problems.
Until the solenoid is actuated, your manifold is feeding the CV and the reservoir. I'd be looking there first rather than the servo. You've replaced a whole pile of hoses and such, have you tested for leaks?
Back to the stumble.
Have you done the 34 Pict 3 adjustment as per
www.vw-resource.com ? Idle speed around 900-950 rpm?
What type of aircleaner do you run? Paper or oilbath?
Have you played with the accelerator pump stroke?
Have you checked the acc pump volume?
Have you adjusted the acc pump spray nozzle position?
Got a degree pulley on it?
If it is an OG VW one, I would verify TDC location and then set the timing accordingly.
Electric choke opening fully?
Manifold rubbers haven't sprung a leak?
Two sore points on this carb are the passage that feeds fuel from the acc pump housing to the spray nozzle and the passage that the auxilliary air jet is in front of. Both can be blocked or partially blocked and are very hard to clean out.
I'll think hard and see if I can come up with anything else.
Regards
Sean