Actually, fiddling with Type 3 or 4 twin carbs isn't all it's cracked up to be. There is a healthy balance pipe (2 in some cases) that means they run at higher revs pretty evenly even if one is badly out. Idle is a different matter, but really if you can adjust a Beetle's single carb, you can do the twin carbs - there are just two of them.
The mixture screws are adjusted individually, maybe 1/8th of a turn out (richer) than fastest idle. Do one, then the other, then check the first, as they will affect each other a bit. If you get a CO meter (eg Gunson's), it can be done a little easier, but you can get close. If the screw undoes with time, replace the tiny o-ring that seals it.
The idle screws (throttle stops) are adjusted to get a suitable idle speed - again, you need to see a change from each screw before you can be sure you have them about right. A Carbalancer (Gunson's, about £10 - £15) makes it easier to get the same flow.
Don't expect to get the carbs adjusted nicely if the valves and timing are out though!
You also need to check the advance/retard can is working (some do both depending on throttle position!).
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