"Newly rebuilt"?
Who did the rebuild and exactly what was done to it?
Engine specs, compression ratio, cam card, etc?
What distributor and what has been done to it (how much timing does it add with the mechanical curve and VA)?
Tuning goes far beyond simply adjusting the APT screw. You have to have the distributor working correctly and adding the right amount of timing as well.
The carburetors idle system must be set up for the engine, plus the right jets and metering, PP spring, etc.....