The attached picture (new clone vs original AFB converted) is of different CFM carburetors but the primary design change by the clone maker is a curiosity. It could simply be motivated by "cheaper to make" reason more so that any improvement in performance. Anyway, I'm sure the add-on conversion came about because "this is the way the clone maker did it" whether good or bad. My first thought was of air flow turbulence caused by the restrictors so I discounted it but I hadn't considered that at lower RPMs, it may not have as much of an affect. The design could well be poor at WOT especially on a racing V8. Sorry for distracting the discussion.
"Adding CFM to a truck will only help at engine speeds you don't want to use." "I found there was nothing to gain beyond 400 CFM."
