Quadrajet - Carb Rescue, Part 2 - Super Chevy Magazine

Sucp 1210 01 Caburetor Repair Carb Rescue Part 2 Quadrajet

In part one of our Carb Rescue story (Super Chevy July 2012) we showed how even a grungy, oxidized Holley Double Pumper carb that had been sitting inactive for decades could be brought back to as-new condition by the Holley Custom Shop. Tech Greg House stripped our old carb down, cleaned it up, replated the main body, bowls, and base plate, then reassembled the air/fuel mixer with all new parts.

This time around Greg will be handling the second most common and popular carb for classic Chevys, the Quadrajet. Rochester first came out with the Q-jet in 1965, as a replacement for the Carter four-barrel carbs previously used by Chevrolet. Unlike the standard "square bore" carbs before it, the Q-jet used a "spread bore" design, where the secondaries were much larger than the primaries, offering performance and economy advantages for base and performance factory engines. The Q-jet would remain GM's go-to carb until the late '80s, when fuel injection in various forms retired the carburetor from O.E. use.

For the street, the Q-jet is a great carb, offering cruising economy with its smaller primaries, but instant performance when the large secondaries kick in. Though they can be more difficult to tune than a typical Holley because of the extra internal parts and design, in the right hands a well tuned Q-jet is a solid performer. Follow along as we get our Quadrajet back into fighting trim.

1 We got our Q-jet from eBay, and this is pretty much how it looked when bought. This carb is the numbers-correct part for a '74 L-48 Corvette, which it's destined to go atop. A Q-jet has more external and internal parts than a Holley, so take note of where everything's at if you disassemble yours before sending it in for rebuilding.
1 We got our Q-jet from eBay, and this is pretty much how it looked when bought. This car
2 After separating the baseplate from the main body, Greg started by grinding off the heads of the rivets holding the butterflies onto the main shafts so they can be removed.
2 After separating the baseplate from the main body, Greg started by grinding off the hea
3 With the butterflies removed, the main shafts can be pulled out. Sometimes these can be difficult to remove if the carb's been sitting a long time and the shafts have seized up. But the Holley pros have a few tricks to overcome this difficulty.
3 With the butterflies removed, the main shafts can be pulled out. Sometimes these can be

4 Once the main body and baseplate are fully disassembled, they're put in the blast cabinet and thoroughly cleaned. A Q-jet has many more nooks and crannies than a typical Holley, so the cleaning process needs to be more thorough and detailed.
4 Once the main body and baseplate are fully disassembled, they're put in the blast cabin
5 Here's the main body after blasting, and before it goes to the in-house electro-plater for replating. Because of the environmental hazards involved with electro-plating, not many shops can still perform this process. The advantage of going to Holley is they can, meaning your carb will look just as it did when new.
5 Here's the main body after blasting, and before it goes to the in-house electro-plater
6 Here's the freshly electro-plated main body with the tumble polished baseplate.
6 Here's the freshly electro-plated main body with the tumble polished baseplate.

7a Reassembly begins first with the baseplate and the butterfly shafts...
7b...butterlies, and throttle linkages being reinstalled.
8 Next up, the new float mechanism and metering rods are installed, then put on the flow bench for testing and initial adjustment. With all the extra internal moving parts on a Q-jet (versus a Holley), this part of the rebuild helps the Holley crew make sure everything is working properly on the fuel flow side of things. This phase also verifies that the main well plugs aren't leaking, and the float moves freely without sticking as the fuel level rises.
8 Next up, the new float mechanism and metering rods are installed, then put on the flow

9a Once that's finished, the top of the main body is bolted back on...
9b...along with the choke plates.
10 Once reassembly is complete, the carb is bolted onto the flow bench and put through its paces to check for leaks and proper function of all linkages, vacuum functions, etc. After that, it's ready to go back on the L-48.
10 Once reassembly is complete, the carb is bolted onto the flow bench and put through it