The Rochester Quadrajet has gotten a bad rap over the years, but it's actually an excellent carburetor once you understand how they work.
Often referred to as "Quadrabog" or "Quadrajunk", many of the issues these units suffer stem from neglect, or "modifications" that do more harm than good.
Being a spreadbore, air-valve secondary design, the Quadrajet is capable of flowing 750 or 800 cfm of airflow, eliminating the need to buy different carburetors when your set-up changes. In addition, the small primaries make for great drivability and fuel economy.
In this clip, I'll discuss theory of operation on the secondary side, since that's where most problems arise. So, leave your preconceived notions at the door and let's see what makes these carburetors tick.
How to debog your Quadrajet part 3
In the first two videos we looked at operational theory of the Quadrajet. In this episode we'll explore a couple mistakes the home mechanic often makes in an effort to improve the performance of this unit.
How to de-bog your Quadrajet part 1
Sorry guys, I got the videos a bit out of order.
The Rochester Quadrajet has gotten a bad rap over the years, often called a Quadrabog or Quadrajunk.
In fact, this is a great multipurpose carbureter once you understand how they work and what not to do to them.
In this clip I introduce you to the Quadrajet and begin explaining the theory of operation of these units.
How to adjust carburetor mixture screws
Here's how to find and adjust the mixture screws on your carburetor.
Note that metering-block style carbs such as Holley and Demon more often have one or 2 mixture screws in each metering block depending on the number of venturi. Also those may not be located at the bottom of the carb as in factory carburetors.
How to adjust Quadrajet/Dualjet fast idle
Quadrajet/Dualjet Rochesters have a fast idle adjustment screw that is separate from the base idle screw.
Here's how to locate it.
Note: Ever since Charter "fixed" my internet and cable after the lightning strike, it hasn't worked right. Go figure. So, if you see this posted then I was finally successful in getting a video uploaded.
750 vs. 800cfm Rochester Quadrajets-how to tell them apart
There exists a ton of misinformation regarding the actual airflow capacity of the Rochester Quadrajet. Not many people know how many variations there are or how to tell them apart.
Here is a simple video explaining how to identify each size based on casting design. I will cover the "cfm-limited" carbs in a separate video.
New quadrajet set up
New air-gap manifold and custom/rebuilt q-jet. Sounds good but I still need to set the timing on the distributor and the carb is tuned already. Hope you like, nothing to fancy just a few revs and walk around...the Exhaust is true dual no x/h pipe and it has cherry bomb glasspacks(3 inch)
More Quadrajet tuning, some things! Part two in this Saga Sept 13, 2010
With the camera sitting on the oil filler cap a few more things to show how a metering rod system works on a carburetor. The car has a slight stumble and surge at a light throttle cruise at about 55 to 60 MPH. By swapping out the .050 metering rods to .048 units, the stumble and driveability concerns are now gone. Going richer would mean worse fuel mileage one may think? No! Now that the mixture is right, LESS throttle opening is needed now, which means higher vacuum, and this way the metering rods will block off the correct amount of fuel, and in the proper timing and percentages, so the car runs much smoother. As stated many times, patience and reading up on, and understanding how these intricate carburetors work will help out very much! Enjoy!