Jerry - one of the many things Carter did to allow tuning of their carburetors was to produce a number of different step-up piston springs. Within reason, the various Carter type YF carbs used on Chevrolet engines can use Carter AFB step-up piston springs, which are widely available.
The Rochester B springs are significantly longer than the widely available Carter ones. We had to expend considerable funds to have the various Rochester B (and 2G/4G) springs reproduced.
Jon.
