2E2 Carb question - 3/4 Point Unit

[VWDino]

Hi,
I have check over a few things on my carb (1.6 Driver) using the FAQ to try to see if I can improve my economy (currently 27mpg on short journeys and 32mpg on motorway runs) and found out that my 3/4 point unit seems to retract fully when I turn on the ignition instead of withdrawing to 8.5mm. It is at the correct extension (14.5mm) with the engine off. Any ideas whats causing this and what the potential consequences are?
Also, what sort of mpg do you think I should be getting? Is mine in need of improvement? Maybe a lighter right foot? 

[rubjonny]

sounds liek a problem with the electrical bits on the rear of the carb, I'd pocket a few from your local scrappy

[VWDino]

Which bits should I be looking for specifically? Any checks I can do to check they're alright? Do you know how the plunger is maintained at 8.5mm against the vacuum?
Cheers for your help.

[rubjonny]

One of the vacuum pipes needs to be blocked, while you suck on the other one
This should retract the 3/4 unit to 8mm.  I can't remember off the top of my head exactly which bit does which, but both of the electrical bits bolted to the rear of the carb above the 3/4 point unit affect its operation so I'd nip to the scrappy and grab both

Problem is carb has to be unbolted from the inlet to get to em, but its not a hard job just 3 bolts