As an update -- I swapped out my HS6 carbs for the ZS carbs
that came with the car originally.

The bog off idle is gone -- 60 weight oil in the dashpots
fixed that. Throtttle response is now quite good.

After that I put in some longer (hence stiffer) piston return
springs the car seemed to be running richer across the range;
it starts easier and seems to be running better.

As far as throttle behavior goes -- from idle to on throttle
the RPMs pick up instantly. Off throttle in neutral, the
RPMs drop instantly to about 1500 and then settle from 1500
to 800 somewhat slowly. I think it's a timing issue with
the advance weights. With the stiff springs and thick oil
in the pots the piston actually goes down pretty quickly.
chris