Re: Edelbrock 1405 step-up springs, which one??
I should have been more clear about my comments relative to idle vacuum, as Vrooom is correct. My comments were intended to ensure that the rods where down or on the lean step at an idle condition so that as you transition to main metering, as vacuum further drops off with throttle opening then the rods still could move up and richen the main circuit. If the rods are up at idle, although your not idling on this circuit, there is no "room" to richen this circuit later if you need it.
As mentioned, major transitional changes cannot/should not be tuned with the springs.
I thought you wanted to play around a bit based on your "all's well" comment. But if this isn't quite the case, get everything else dialed in first.
Vrooom, I like your working theory, I've got to think about that one more to really "get it". When it comes to Edelbrock's comments about springs reacting to load, I think of this as what happens when you encounter a long gentle hill -- not much change in throttle position, operation is pretty close to steady state conditions. I'v come to this idea because Carter had some three step rods on motor home carbs in the 70's -- an application that has a fairly healthy throttle opening at mid-RPM steady state cruise conditions -- they'd run on the middle step. Without it, they'd be on the power circuit.
90 Corvette ZR1
TC# 3094 ACES# 7297