You have to take into consideration the wear on the parts in question. After 30-40 years of service, any adjustments on a carburetor will depend on it's condition, and will not likely respond as expected to stock settings. How will vacuum affect the step-up piston that may be worn to a smaller diameter, and has a bore that may be unevenly worn? How much material is gone from the metering rods, and the jets they operate in? Are the holes for the metering rods in the step-up piston's arms round, or worn oval?
I believe many slantsixers have experienced difficulties when adjusting a BBD after it has dismantled for an overhaul, and I would suggest that the stock settings only serve as a starting point.

Olaf

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Aspenized

Thanks matv91 for the information. I did adjust mine without taking notes. Opps. Rebuilt it and gaped to 0.035. Luckily one can however easily get to the step-up piston for adjustment with the carb on the intake, if need be.

Also, I did find this:
Chilton's Auto Repair Manual 1972-1979 (American Cars from 1972-1979)

Printed 1978 ISBN 0-8019-6914-x

Page U55

Vacuum Step-up piston adjustment (Carter BBD)
"2. Be sure not to disturb the adjustment screw on top of the piston. If it is disturbed, reset the gap at the top of the piston to 0.035-0.040 in."

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exoJjL

Well another way to tell a story.Carb reaches very end of productio line, is hooked to flow meter. Allen head screw is turned from the mean point .035 one way or the other until the numbers come up right on the meter. Each carb flow tested.That,s why the directions say note direction and number of turns.

Closed throttle and .035 gap are used to put metering rod lifter arm and throttle shaft into correct phase. In other words they start out from the same spot. The metering rod lifter arm has both rich and lean piston stops,which change position with throttle position.

Red arrow is metering rod lifter arm. green arrow no gap Low vacuum,heavy load. Step-up spring has pushed piston up to rich limit stop for that throttle position.

Yellow no gap, high vacuum low load. High vacuum has pulled step-up piston down to lean stop for that throttle position.That piston and metering rod arm in pictures are found in 318, slant six different arm and piston less movement.