My experiences with a quadrajet go back some 25 years or so when I built a Stock Eliminator car, a 68 Chevelle with a 327 and a Quadrajet. This thing will amaze you, but it has to be set up correctly, and meticulously maintained. It is a conventional primary with part throttle low speed enrichment provided by a set of primary metering rods that fit inside the primary jets, and are held down by engine vacuum working on a power piston that features a hangar that the primary metering rods hang from at their tops. A large spring in the vacuum well lifts the hangar as vacuum in the well drops upon acceleration. We remove the enrichment spring, remove the rods, reinstall the power piston, and jet the primaries around 73 or 74. A large camshaft doesn't provide the most consistent vacuum signal in the intake at low speeds, and you don't need the rods fluttering and creating an erratic fuel distribution condition at idle or low speeds. A 340 horse cam would provide a strong steady vacuum signal at low speeds, so having a low speed enrichment is a moot point anyway. The Q-J uses a pair of secondary air valves with a mild spring to close them plus the action of a choke pull off to keep the air valve closed unless the secondary butterflies are open causing engine vacuum to override the pull off and the spring. A cam on the air valves lifts the secondary metering rods out of a pair of wells in the carb bowl to provide high speed enrichment. The hangar for the air valves attaches with one screw on the top of the cam, taking the screw out is how to change the metering rods. Metering rods have a long tip with various tapers and lengths, that's how the air/fuel ratio is adjusted as part of your tuning. Both carburetors should be a matched pair, a mis match here would cause all kinds of mysterious stuff to happen. Both carbs will probably like to be adjusted the same, and there is no reason not to use all four idle adjusting screws simultaneously. The 340 horse cam might prove to be too mild for a pair of four barrels, it was designed for one carb smaller than either quadra jet. The Chevy carb is the only way to install dual carbs on this motor because of the fuel inlet location. The carb number for my stockers is a 7029207. All three cars have the same carb, they works pretty well. The beauty of that carb is its simplicity. The 327 Stock E camshaft has .390" intake lift, and .410" exhaust lift.It has around 260-265 degrees duration at .050", this thing sounds like a jack hammer breaking concrete at around 2000 RPM, but you wouldn't want to drive it on the street. Too radical and valve train parts longevity would be an issue. I've never tried running two of them together, but nobody ever succeeded by not trying something new.
Seriously, my tuning parts are down to some Edelbrock and Quick Fuel ( holley ) parts now.
