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.

 


The following photos show the change from the AFB to the Q-Jet, which took place in August of 2004.

 

This is the old Carter 9625 AFB that someone once gave me in 1987 for free. Notice there is no choke assembly, which makes it somewhat tricky to start even during the summer. At least I didn't have to worry about my wife sneaking off with it.

 

Edelbrock spreadbore to squarebore adapter. This adapter is made to mount spreadbore side down. Notice the bump on the gasket on the bottom right-hand corner. It corresponds with a bump on the adapter's bottom left-hand corner. I'm sure it was one of GM's better ideas but the carb does seem to seal well in spite of it.

Offenhauser makes a spreadbore to squarebore adapter (PN 5816-R) too but theirs is designed to be mounted spreadbore side up as we are intending to do. If I would have seen the Offenhauser catalog when I started this project, I might have used one too.

 

Spreadbore adapter mounted on the Offy intake. This adds 3/4" to the height of the carburetor but keeps a separate pathway to the intake manifold for each carburetor barrel. There are open plenum adapters available too but I wanted to keep the plenum volume as small as possible to minimize any chance of off-idle bog.

I had intended to install a 1/2" insulator between the adapter and the carb but found that I just don't have the head room for it with my Corvette air cleaner. The Offy-supplied mounting plate is 7/16" thick so you would gain an extra 1/16" clearance over the plate I am using.

 

I like the Quadrajet carb because of the small, double venturi primaries and because they were so plentiful in the junkyards. I happened to have this one surplus from a 1977 Pontiac I converted to propane in January of 1998.

The other thing I like about this carb is the small central fuel bowl. I found that the AFB was sensitive to fuel level in the bowl and had a loss of power on hard left turns. Of course, after I raised the fuel level, this problem improved somewhat. The as-installed Quadrajet has no apparent sensitivity to turns in this orientation.

 

I was at a speed shop back in the 80's when some kid replaced the stock air cleaner on his Corvette with one of those shiny chrome ones. I gave him $10 (Canadian!) for it and have been waiting for an opportunity to use it ever since.

 

With everything assembled, I have about 1/4" of clearance between the hood and the top of the air cleaner lid. I knew the kids' play dough would be useful for something other than for making a cat's birthday cake.

When I first took the car out for a spin, it seemed to run at least as well as the AFB and this is with the carb set up for a Chev 350. Since the carb has been sitting in my garage since 1997, a good rebuild probably couldn't hurt. I know the sound the carb makes when the secondary air valves open up on the 350 but I didn't hear it anything like it on the short drive I made to test it. I got out onto the QEW and took it up to about 90 mph but ran out of highway as I only went from one interchange to another.

Notice the two marks on the hood as the air cleaner was rubbing on it. If you look at the previous photo, you can just see where the paint was worn on the air cleaner lid. Looks like I'll have install a lower profile air cleaner.

 

I extended the air cleaner hold-down stud up to the hood and marked the contact point. From that point, I measured a radius of 6¼" to the hood bracing which means a maximum allowable diameter of 12½". The height of the the Corvette air cleaner is 3-3/8". For aftermarket, I think you would be safe using a Mr Gasket 9" diameter assembly which is only 2¾" high but I haven't verified if this would work. There are smaller 6" diameter by 2" high ones too but think these are more restrictive.

I took a walk through one of the local junkyards and found an extremely short air cleaner in a 1984 Firebird. The lid diameter is over 14" so it hits the bracing.

 

The Firebird air filter diameter is less than 11-3/8" and the height is 2½". After an afternoon with a saber saw and some black paint, I got an open-element air cleaner with a 12" diameter lid. There is plenty of hood clearance now with the Firebird air cleaner so I will try adding some heat dissipators later.

The air cleaner I found had a collar on the inside diameter of the air cleaner pan. I think its only purpose was to limit horsepower on the Firebird so be sure to remove it for a free-flowing air cleaner.

I got the electric choke conversion working but found that there wasn't a good ground from the thermostat housing. A short length of wire to one of the carburetor studs fixed that problem.

 

Notice the blue hoses going to the bottom of the intake manifold. I got my prototype intake manifold heater installed at this time too.

 

A close-up of the intake manifold heater. This device has completely eliminated the off-idle bog. The Quadrajet seems to pull a lot harder than the AFB but this is my seat-the-pants feeling. I'll have to go to the drag strip to know for sure.

With the open air cleaner, I can hear the air valves opening up now. With a flow capacity of 750 CFM, the sound is not quite a loud as I was used to with the much larger Chevy. They do, however, seem to crack open quite frequently while I'm cruising on the highway.


In June of 2006, I noticed that my right front wheel cylinder was leaking.  This was a good opportunity to switch over to disc brakes from the 1974 Duster I got the year before.  Unfortunately, the brake conversion dragged on until June 2011.  After 5 years, I had a hard time getting the car started and, once running, the old gas in the tank plugged up my fuel filter and the crud may have caused the float valve to leak.  In July of 2011, I had to reinstall the AFB because the carb was overflowing gasoline onto the ground.

I thought that now would be a good time to rebuild it to rebuild the carburetor and club members recommended Specialty Carburetors Inc. in Toronto.  Over the winter, they restored the carb to factory-new condition, including rebushing the shafts and going down one primary jet size.  They told me that the Edelbrock electric choke was a piece of junk and replaced it with a GM unit.  I dropped off my AFB too to get refurbished with a choke assembly but they told me not to bother because it was full of rust from a rusty gas tank.

I wasn't ready to replace my gas tank just yet but gas tank rust is very fine and the fuel filter was not enough to keep it out out of the AFB's fuel bowls.  After shopping around, I got a new Spectra CR11F gas tank through Rock Auto in October 2013.  I am still amazed that this Canadian-made part was far cheaper to order from a Rock Auto warehouse to Buffalo, NY than it was to buy with a trade discount from the local NAPA store.

I tackled the tank replacement in 2014 after the fuel line ruptured at the electric fuel pump on our way back from Canada Day in NOTL and I lost about a half tank in the 15 minutes it took me to get home. While the tank was out, I noticed that the filler tube and sender were rusty.  Replacing the sender was easy but the filler tube was more of a challenge. Removing the tube was a fairly big job because the left rear interior around the trunk interior needed to be disassembled.  I ended up removing the filler tube rust with a chelating solution (Evapo-Rust) and then coating the inside with POR-15 tank sealer (1 pint was plenty).

 

I also took the advice of club members to clear-coat the tank before installation so as to maintain a new appearance, which was another delay.  To ensure that my fuel sender would work properly, I thought it would be wise to add a ground stud to the sender, which I sealed on the inside with epoxy. I got sender with the larger 3/8" fuel line to match my previously upgraded 3/8 fuel line and the 1/4" nozzle was for future use in case I ever got around to fuel injection.

 

 

It took me until October of 2015 to get the car back on the road.  I continued using the AFB to ensure that any residual rust in the fuel lines would not foul my newly rebuilt Quadrajet.

While driving around with the AFB, I revisited the primary jetting and improved the car's fuel economy.  It ran pretty good but the lack of choke and the left-turn cut-out was still a bit annoying.


With the good weather persisting into fall of 2016, I decided that November 13 was going to be the day I reinstalled my Quadrajet.  The first thing to tackle was deleting the 1-7/16" high collar spot-welded to the air cleaner's pan.

 

With pan painted black, it's hard to see the collar but, after comparing 2004 1/8 mile times at Lancaster, running with the unmodified air cleaner was definitely slower than with no air cleaner.

 

There were 4 spot welds holding the collar on.  One weld was not easily visible and I guessed at its location but was off about 1/4".  I used my die grinder and went through 5 bits in the process. My wife is very understanding and didn't complain too much about the fumes when I used the oven to bake the touch-up black paint.

 

After taking the AFB off, I was once again looking at my 90° carb adapter.  The studs that hold down the carb are locked with nuts under the adapter.  I had to remove the nuts so I could install bolts in the outer holes to hold down the adapter.

 

I got rid of the large heat shield because it make it much more difficult to install the spreadbore adapter bolts.  I had my doubts that it was providing much benefit and I used a gasket-shaped heat dissipator plate instead.  I exchanged a pair of short studs for long studs at this time. Depending upon whether the carb runs hot and available hood clearance, I may have to use longer studs later.

 

The Quadrajet looks pretty good back on the slant six.  It took some work to get the car running because the idle mixture screws were turned in and the car would stall as soon as choke started to open.  I also had to bend the throttle bracket forward because I couldn't reduce the idle speed otherwise.

 


The following is a list of parts to install the Rochester Quadrajet on your six cylinder car.

MANUFACTURER PART NUMBER DESCRIPTION
Offenhauser 5270LK Intake Manifold
General Motors from 4bbl -V8 cars Quadrajet Carburetor, air cleaner, throttle linkage
General Motors from 4bbl -V8 cars 1984 (third generation) Firebirds and Camaros (verify dimensions first!)
Edelbrock 2696 Squarebore to Spreadbore adapter (install inverted)
Offenhauser 5816-R Spreadbore to Squarebore adapter (for primaries forward)
Edelbrock 1932 Hot air to electric choke conversion kit (may need to add ground).  Take your chances with this or get a GM part.
Edelbrock 1991 (74 & earlier)
1992 (75 & later)
Race calibration kit (metering rods, jets, etc)
Mr Gasket 1487 Chrome 9" diameter air cleaner, 2¾" high. (Clearance not verified!)
Mr Gasket 97 or 86 (1/4")
98 or 86B (1/2")
Heat dissipator (if you have the hood clearance and you want to keep your carb cooler)
Mr Gasket 3704 Vacuum Cap Assortment
Any (for fuel line) 3/8" to 5/16" brake line bushing
Any (for fuel line) 12" to 18" of 5/16" ready-made brake line
Any (for fuel line) 2" of 5/16" rubber fuel line & 2 gear clamps
Any (for vacuum) 1/4" NPT pipe plug (to plug vacuum line to GM transmission)
Any fasteners assorted 5/16" nuts, bolts, washers, studs

Since I have already had a transmission throttle linkage in place which was working for the AFB, I didn't need to fabricate a new one. I researched the installation of a Lokar throttle linkage and they have the parts to make this carburetor work with the Quadrajet. Check with first before buying any parts, just to be sure!

The following is a list of Lokar parts to install the Rochester Quadrajet on your six cylinder car.

PART NUMBER DESCRIPTION
SRK-4000 Universal throttle cable bracket & springs
TC-1000U Universal black throttle cable
KD-2904U Chrysler A904 automatic transmission kickdown cable
Gas Pedals Pick one to suit your style

If you want to go instead with the stock GM throttle cable, brackets, and gas pedal, you can easily fabricate a bracket to mount the kickdown cable by itself.

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