[TR] zenith or su's ?

[Anthony Rhodes]

>You don't want to compensate for bad Needles with Springs. The Needle
>Profile or what Jim called "calibrated" is the
>most important part. Sort the Car out on the road using the Volvo Needle
>then see where you are rich. At idle or popping on the Highway.
>Then take it from there. The Springs should be your last concern.
>Wayne

Wayne,

I'd say that you need to figure out your spring first, since it (as you say)
determines which part of the needle profile is operational at any given power
level (and controls the amount of "constant depression").

The way to determine this? Not simple.  You can guesstimate it from the spring
used on other cars with similar HP and carb choke size.  You can directly
determine it by looking for just reaching full piston lift at maximum flow
rate.  Unless you get a child to ride alongside the engine as you race down
the road, I suppose the only way to do this is on a dyno.

Excessively strong springs will work, but will cause greater restriction on
air flow than necessary.  I.E.  you have smaller choke carbs!  Excessively
weak springs will also work OK, until you get to maximum lift.  At that point
you lose the ability to control the misture with the needle, and the mixture
is determined as if the carb were a fixed choke type.  Mixture will be
dependent on airflow to some degree.

Of course you will have to select different needles for the different spring
rates.

-Tony