From Jenvey's site:
Balancing throttle bodies
Idle bleed screws (if fitted) should be closed at the start of this operation.
Before starting the engine adjust throttle balance by setting the single idle adjuster screw so that the nearest butterfly
is just visibly open, then adjust the cross-link screws so that the remaining butterflies are at a similar angle.
Start the engine and use a flow meter (SYNC10) to check airflow through each throttle body bore, adjusting as
necessary. It may be necessary to re-adjust the idle during this process. Always re-check the balance on all bores
after each adjustment and with the cross-link adjuster locking nuts tightened. Idle bleed screws (if fitted) may now
be used to balance ports on twin bodies.
What are the cross link screws? The small bolt and port just next to the injector ports are for idle air. The small screw just in front of the injector port is another passageway into the throttle body, and isn't linked to the butterfly valves themselves.
From 20 minutes of staring hard at the throttle bodies themselves: It looks like all we need to do is set the bump stop on the primary twins, then adjust the loop on the secondary twins to match the two assemblies. Then adjust idle air to match flow rate for each individually using the idle air bypass screws that are right next to the injector ports. Or if you are awesome, you can use an IAC valve plumbed to all 4 ports (so even idle air and it will always remained balanced).
Do we change the angle of the butterfly valves themselves individually? OR are they all already matched, and all we do to balance them is adjust idle air bypass?
What is the 1.6 OEM fuel setup (single fuel supply line to fuel rail, FPR mounted to end near no. 4 cyl, fuel return from FPR)?
Can we use another Fuel rail (rather than the 3 piece fuel rail that comes with the jenvey kit)? Is the injector placement the same as stock, so we can use something like the M-tuned fuel rail from 949?
CND, what's your vacuum setup (what size fittings, tap, tubing you used etc.)