Holley 750

i always set the timing first, then set the idle speed and idle mixture using a vacuum gauge to get the highest vacuum reading then fine tune the idle from there until by ear. i usually set the timing with a combination of vacuum, timing light and by ear until i have it just right. i can tell you already you are going to get a bunch of different answers because everyone does it a little differently.

Before any carburetor tuning, the fuel bowl float level must be correct. If it's not, it might sound and look good on idle, but will pop or backfire when driving.

Starting point for the idle mixture screws ( these are on either side of the main metering block) is usually 1-1/2 turns. And don't think these are more than idle screws. They have nothing to do with the mixture once the carb has transitioned to the main circuit. The main jets (and secondary jets if it's a 4150) control the mixture once the engine's off idle. (in addition to the powervalve and air bleeds.) To figure what's the best fuel/air mix you either must use a Fuel/Air meter or learn to read the spark plugs. The meter is more precise and faster, but it cost's you nothing to read the plugs other than labor.