Technical Carter/edelbrock step up spring ratings

Are the springs for these carbs rated at the point where they start to open, or where they finish opening? In other words, if a spring is rated at 5" of vacuum, I could see that meaning:

(A) the metering rod starts moving up from the bottom position at the rated 5" of vacuum and completes movement to the top position at, say,, 3" of vacuum.

(B) the metering rod starts moving up from the bottom position at, say, 7" of vacuum and completes movement to the top position at the rated 5" of vacuum.

Also curious how much "range" there is for a given spring between when the metering rod starts moving up and when it completes movement, is it like 2" or 10" of vacuum difference on the tapered portion of the metering rod?

 

I have an original Carter book that may explain all of this in the AVS/AFBs. Want me to send you a copy of the appropriate pages that applies?

 

I'm not sure a mathematical equation is going to tune the carb, springs are cheap and experimenting with them is your best route.

 

@carbking, if anyone knows it’ll be Jon

 

The springs are rated at when the force applied by the tension of the spring begins to overcome the force applied by vacuum.

I have never seen anything about a "range".

As Swade mentioned above, it is just a reference point. Testing different springs is the way to tune.

Jon