Okay -- my understanding of carbs like SUs and Strombergs is a little
shakey.

So far as I understand, there are several variables. Things like needle
taper and orifice size make sense to me. The air flow causes the piston
to rise raising the needle and allowing a certain volume of fuel to flow
in -- the higher the needle the more fuel.

Pretty simple, right? Well, the part I don't quite understand is how
the spring rate and the damper fluid play into this.

A heavy fluid keeps the piston from rising quickly. I'd assume that this
will cause a lean condition under a "throttle opening" situation where the
leanness will persist until the piston can rise to the correct setting.
I've been told, though, that what actually happens is that the piston stays
lower, the air velocity increases, and this brings in more fuel. Now I'm
confused... Also, there is the spring -- I'd assume that the stiffer the
spring the leaner the carb will tend to run over the whole range except
at maximum air flow, where different spring rates will not matter a whole
lot. How does the spring play into this?

So what's the straight poop? I'm specifically asking because I just put
some zenith strombergs onto my 164 (back onto it, actually, since they're
the carbs that came with the car at first) and the car goes dead lean
just off idle when I hit the gas. I'm using "SU" damper oil in the pistons
and I don't remember the characteristics of the springs I've got in the
carbs, except that they match.
chris