[tekuhn]

I hope you don't mind me jumping in here with what I think are questions related to the subject being discussed. I do not have a bathtub intake, but I am building a pair of SD clone carbs from a pair of 2840S AFB's ('59 Buick 401). My biggest concern is regarding the weight of the secondary air flapper valves. Seems to me that with half the volume of air passing through each carb at any given RPM (compared to a single carb), it's going to require considerably more RPM (twice?) to fully open the air valves.

Any thoughts on how to go about scientifically and methodically fine-tuning the air valves? Is the shape of them all the same and the only changes are to the counter-weights? Perhaps you do indeed want to delay the secondary air valve opening somewhat in a dual carb setup to avoid low velocities and poor atomization?

The jetting can be worked out in a straight-forward conventional manner, but the transition of the primary circuit enrichment for decent street manners is another matter. I think getting the spring just right is going to be hard.

I'd appreciate any and all thoughts and comments.