A Quadrajet is an excellent carburetor for a mild to moderate street engine.

There are a couple important things that need to be done to it.

One, you need to adjust the opening rate of the secondary air valve. From the factory, they usually take 4-5 seconds to open. For best performance, you want yours to open in about 1-2 seconds. To rest it, connect a Mityvac vacuum pump to the secondary air canister. Apply about 15 inches of vacuum. Release the vacuum and use a stop watch to see how long it takes for the canister to extend all the way. There is a metered orifice at the vacuum hose inlet to the canister. To adjust the opening rate, drill out the orifice with a 1/8 inch drill bit. Next, take a wooden or plastic golf tee, and cut the head off it. You will drill a small hole through the golf tee, and slide it inside the vacuum hose between the canister and the manifold vacuum source. You can try using different drill sizes until you get the opening rate that you want. I think I ended up using about a .055” drill bit with mine, I can’t remember exactly. Doing this will eliminate the famous Quadrajet “bog” that so many people complain about.

The other important thing to do is to adjust how far the primary metering rods are inserted into the jets during cruise conditions. Late 70’s Quadrajets are the best ones to have, as this is a pretty simple adjustment on them. There is a plug from the factory that you have to remove in the top of the carburetor. This plug is directly over the power valve/primary metering rods plunger. Tap out this hole so you can install a 1/8” pipe plug in it later. Warm up the engine, and run it at cruise RPM, say about 2800 RPM. You can stick an adjustment tool down through the hole and turn the APT (adjustable part throttle) screw until you get the smoothest running and highest RPM. Now the cruise mixture is set correctly for your engine combination. This will likely be richer than it was set from the factory for the smog engine.

There are plenty of other little adjustment you can do to fine tune a Quadrajet, but starting out with these two will get you very close. I use a Quadrajet on my Chevy 350 T Bucket, and the throttle response is fantastic. It just takes some patience and experimenting to get it right.