More Quadrajet tuning, some things! Part one in this saga on Sept 13, 2010
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!
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!
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
Replacing an HEI Coil & Quadrajet Comments (Not a "How-to")
The '77 Olds 350 suddenly developed a pretty nasty miss under load, which
slowly worsened to a miss at idle too. If you got close to the distributor
with the engine running, you could hear the coil arcing all over the place!
The Delta is equipped with the usual GM HEI distributor.
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.
See 1976 Chevrolet pickup with Rochester quadrajet upgrade on SBC 350 V8.
We removed the hood, mounted a camera looking down on the air horn, and
took it for a spin, running wide open on an uphill grade. See how the
secondary air valve responds to rpm drop at each upshift of the THM. Also
included is a smoking burnout.
Leaky RV carb
Carb in my RV leaking around accelerator jet. looking for ideas as to where
the leak is starting and what needs to be fixed.
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.
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.
Quadrajet air leak fix and warped air horn repair tutorial.
How to identify a Quadrajet with a warped air horn without diss assembly or
running it on a car. These tips would have saved me time and money which is
why I made this video. I also discus how to repair a warped air horn and
prevent your air horn from warping in the first place. If you have a
whistling noise just off idle then you got some work to do. You will never
get your engine tuned right, your cold start performing or decent fuel
economy unless your four barrel carburetor is just right. Special thanks to
Cliff Ruggles for his book Rochester Quadrajet carburetors and to my
brother Adrian who spent hours on tuning and fitting.
See this video for description of the technique I used to straighten a
warped air horn.
here is a technique for re-bushing the throttle shaft without drilling.
How to de-bog your Quadrajet part 2
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
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.