Tuning my 383 4bbl...have a couple of questions

[StockMan]

I have a 383 4bbl with a 4401 carter and am in the process of doing some fine tuning and have a couple of questions.  I'm fairly new at this.

I have a vacuum gauge hooked up to the vacuum tree on the intake and have all other vacuum sources plugged.  I don't have a tac yet so I'm estimating the idle at around 800 or so.  I would like to properly adjust my ignition timing and air/fuel mixture.  I haven't had the chance to ensure that TDC on the timing tab matches actual TDC, I guess this would be a critical step. 

Vacuum sits at about 12 and is steady, I have to really idle it down to make it go below 10.  Idling up makes it go to 15-16 immediately.  (Note that I have a slightly longer duration on the cam)

I adjusted timing (with the vacuum hose off and plugged) to approx 5-6 degrees on the 'Before' side of the zero marker on the timing tab.  I then plugged the vacuum line back on and noticed no difference in idle speed.
  Question: if I go beyond 6-7 degrees the motor wants to idle up??  Why is this?
I hooked the timing light back up and raised RPMs gradually, timing changes almost immediately moving up from the 6-7.

Now I adjust the driver side screw on the carb, turning it in until the motor begins to stumble, then I turn it out until I see max vacuum and a smoother idle.
I make the same adjustment on the passenger side screw.
  Question: Do both screws need to be set at the exact number of turns out or do I leave them?

Question:
From what I've done here would I be relatively close in timing and air fuel mixture?
How does on adjust the larger screw on the upper part of the carb?  I have it set at 1 turn currently.
Are there any other steps I can take? 

Thanks

[Kevin68N71]

I have read in some Carter manuals that you start with a minimum turnout of both mix screws at the beginning, then tune as you suggest but move BOTH screws the same amount.  I have tried and played around both ways and just "super tune" and play and play until it is just right, driving the car between rounds.

Like a good Ferrari mechanic, it's all in the sound I believe.  I do not know if the above applies to all carbs.  Sorry to muddy the water further.....

[Big Lebowski]

  When you get good at it, you'll toss the timing light and set it advanced to the point where there's no bog while you're throttling it. If it's hard to start, at that point you just back off the advance a teeny bit. The carb. mixture kinda depends on your gas octane. Put 87 octane crap in a 10-1/2-1 big cammed 440 & it won't run very good. 

[StockMan]

Thanks.  The 383 I have has 9.2:1 ratio with the 4bbl intake and 4401 carter carb.  I have mid grade fuel in it.  It running very nicely and I pulled a couple of plugs and they look good to.  I guess I need to wait until I can drive the car before doing any further tuning.