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 HP for $40.
A GEARHEAD PRODUCTION. Throw away the Edelbrock and the Holley and save
your money. You can build a hp QJ for less, and get better performance and
Identifying Quadrajet vacuum ports
I always see a lot of questions about what various vacuum ports do on a
Here's a general guide that will point you in the right direction.
Remember that there were many different Qjets over the years and vacuum
port locations and number will vary. This video is representative of
Combination valve bad, carburetor bogging
After doing the brakes -- the combination valve is bad-- the valve part is
seized. Troubleshooting the bogging...
Gapped plugs, plugged vacuum lines, check carb mounting bolts, distro shaft
has no wobble, the mechanical advance seems good (I guess-- moves freely),
accelerator pump squirts well
How to measure and adjust Quadrajet float level
I have had several requests for this, so here you go:
1. The airhorn has to be removed to do this, but the carburetor does not
have to be removed from the engine.
2. Some data says to measure from the toe(end that is opposite from the
hinge), some say 5/16 inward from the end, etc. I suggest following the
specs for your particular carburetor.
3. With the float in the raised position and the inlet needle lightly
seated, measure from the top of the float to the top edge of the carburetor
with NO gasket in place. If you have to adjust the float, bend at the area
that has the cutouts,
4, If you are experiencing flooding issues then it is an excellent time to
install a new needle/seat and float and that should cure flooding problems
that are not choke-related.
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.