Holley carb prob ...or not?

Hi, Just found this site and hope I may find some answers to my Street rod problem.
I have a small block chevy 283 with Gm Hydromatic 350 trans.
Problem is a stumble during hard accelleration from idle or during cruise. I have a Holley 1460 carb on a spread bore Holley intake.
Carb is about 10 years old. Ignition has been updated to a new Pertronix distributor but did not help the symptoms. I read where backfires thru the carb will blow the Power Valve so I pulled the carb apart and gave it an overhaul this weekend. Replaced Power valve and put in a Summit kit to protect it from blowing again. Lucky cause it still backfires thru the carb. Valve was replaced with same value 6.5 as original. I left the Jets the same as I don't know what I am doing yet. I wrote down jet size, squirter size, accelerator pump cam size etc... so I can answer those type of questions if needed.

A couple of quick questions then I will let you all (yall) as me some.
1. To change the acc pump cam from position 1 to 2 is there just a very littly movement from one position to the next? Do you have to flip it over or what?
2. The "idle adjustmet screws" on either side of the meter block (I only have one on the front) How should these be adjusted ? and if I turn them in one at a time till they bottom out should I be able to "kill" the engine? The one on the driver side doesn't have much effect.
3. I took a vacuum reading off the manifold while at cruise and mild uphill climb, right at the carb base, and as best I could figure I chose a Power valve that is a couple of steps down from that/those readings. It seems like a crap shoot though to get a reading that is stable. What better way is there?

I've done a bit of rambling here and tried to include some of the things that may be important, but who knows I may be real lost and need to be led by the nose to solve this.
If anyone has suggestions as to what is my next best step I would appreciate it a great deal.

Thanks a bunch in advance.

Kim