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
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 THAT THE CHOKE ITSELF MUST BE WORKING IN ORDER FOR THE FAST IDLE TO
how to minimize engine bog with a Quadrajet carb
this is to minimize engine bog when the pedal is to the metal. do not over
tighten, very small spring...you want to try 1/4 turns or 1/2...q-jets are
good if tuned properly. also when you are tightening screw it will have
tension on it so keep the screwdriver firm. 1986 gmc sierra single
straightpipe to cherrybomb. you will need a small flathead screwdriver and
a 3/32 allen key. be sure not to tighten to much or else your vacuum
secondary flaps wont open.
Rochester Quadrajet, the results!
Two mishaps, the first shown here, the choke coil I got was wound
backwards, it made the choke butterfly wind up TIGHTER as the engine warmed
up. I swapped on the one from the old carburetor fast enough, the second
mishap made me feel like a crud and what did I mess up later that evening.
The car would not start leaving the Etobicoke -Queensway show. It was not
getting gas. We got it running by priming the carburetor, and boy, was I
ticked at myself. In the end it was not my fault it looks like. The new
accelerator pump umbrella and rod was a very poor and frail design, the
umbrella came detached and stayed at the bottom of the of the pump well,
and was a distressed mess. The maker will get a note from me. The upshot?
The old assembly went in, all is perfectly fine, the slight tip-in
hesitation is gone now too. Stupid lack of pride it seems these days
making parts for even simple things like an old carburetor.