APT adjust vs metering rod swap

[CJK440]

I understand how APT physically works, adding adjustment to the power piston down stop to change the relationship of the tapered part of the metering rod to the jet at full manifold vacuum in order to adjust low load cruise mixture. My understanding is that it is more of a fine tune than a replacement for rod swaps.

It seems to me I would want to set my APT to a "start point" then swap rods for best cruise and then fine tune with the APT screw. But what is the magic "start point" for the screw adjustment. I have seen a figure of .020-.030" of brass showing above the plastic retainer with the spring removed. I imagine whatever this setting wants to be where there is a tapered part of the rod in the jet so adjustment + or - is possible.

[Cliff Ruggles]

The first step in tuning is to determine the correct jet size.

Then use primary metering rods with a tapered upper section for tuning in the "normal" driving range or light load when the PP is down.

Since metering rods used in the later carbs will either have .026" or .036" tips, there are primary rods available so the APT can be set up for full control of part throttle A/F from rich to lean without taking the carb apart and changing them......Cliff