Join Date: Dec 2012
Location: Gastonia, NC - Born & raised in Connecticut - 31 years
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4248S shows up as a 1967 285HP 326/automatic on the Firebird & Tempest/GTO having A.I.R.(Air Injection passages for the exhaust - Smog equipped engines).
4034S shows up as a 1966 335HP, Block Code YS, 389/automatic Tempest/GTO, non A.I.R. engine. Also used on 1966 B-Body 389/automatic cars.
That said, the carbs are engine/trans specific, with and without A.I.R. passages, and most likely fitted with application specific internals such as jets, step-up springs/metering rods, and idle-air bleeds.