I bought my 1965 Barracuda on June 7, 1983 and it was equipped with the original 225 slant six and Carter BBS 1 bbl carburetor. Like many other young men, I wanted to give my car a bit more power so I followed the Chrysler racing manual's (PN P4286519) and Direct Connection catalog recommended engine modifications.
One of the modifications was to upgrade to a 4bbl carburetor and the racing manual suggested the Carter AFB 3854-S (1965 & later 273s) or 4294S (1967 273, 235 HP engine). Many people like the Holley 0-8007 carburetor (390 CFM, vacuum secondaries) in this application but I preferred the AFB because I thought that Holley's side-hung fuel bowls were an inferior design (spill gasoline with every jet change). I can change metering rods and jets on an AFB mounted on the engine without spilling a drop of gasoline. There are a number of other technical advantages that the Q-Jet has over the AFB but an important one is the small primary venturis from the spread bore design. The practical advantage is that Q-jets were installed on thousands of cars in the past decades and should still be relatively plentiful and cheap to acquire.
Being a poor student at the time, I opted instead to use a Carter 9625 AFB that someone gave me for free but did not have any choke mechanism. The 9625 AFB was a bit big for a 225 CID engine (625 CFM) but, since the secondaries are closed most of the time, the 9625's primaries are comparable in flow to the Carter BBD 2bbl carburetor. I installed the AFB in October of 1987 and, over the years, I was able to find a metering rod and jet combination for the primaries that gave me both great power and better fuel economy than the old BBS 1bbl carb. I never got around to sorting out the secondary jetting.
Upgrading to a 4bbl carb does make a large increase in performance. If your full-throttle manifold vacuum is higher than 1.5" Hg, you can probably use more carburetion. Originally, the car did a 19.0 second 1/4 mile with the Carter BBS 1bbl carb, automatic transmission, and 2.93 rear gears. Upgrading to headers, a Direct Connection high lift, short duration cam (PN 4120243), 318 valves, 340 valve springs, and some mild porting, the 1/4 mile time improved to 18.5 seconds. Installing the AFB (jetted for a Chev 350) resulted in a best time of 17.078 seconds @ 81.96 mph.
As I had already upgraded from the OEM Carter BBS one barrel carb to the AFB using an Offenhauser 4bbl intake manifold, the manifold is still suitable for the Q-Jet. However, with the intake being drilled for a square-bore carb, an adapter was required to make the new carb fit. Luckily, Offenhauser and Edelbrock have adapters that allowed the new Quadrajet to be a bolt-on upgrade.
To get better front-to-rear fuel distribution, I mounted the AFB so that carburetor shafts were parallel to the engine with the primaries facing away. I felt that this allowed the primaries to be roughly equidistant from each of the cylinder. Mounting the primaries closest to the engine would have meant that cylinders 3 & 4 were closest and 1 & 6 were farthest. Checking the sparkplugs' color over the years, I think my reasoning was valid. Although the AFB has baffles in each of the fuel bowls, its design allowed gasoline so slosh away from from the primary jets on left turns with this configuration.
The Offenhauser's original carburetor mounting plate had the primaries facing forward. To get that symmetrical fuel distribution between the front 3 cylinders and the rear 3 cylinders, I made a carburetor mounting plate for the Offenhauser intake manifold which turned the carb 90°. Offenhauser probably supplied it that way to simplify the fabrication of the throttle and transmission linkages. I had to fabricate my own throttle linkage for the new arrangement.