Electric Choke adjustment: rich and lean extremes
In this video, I am purposely changing the rich/lean adjustment wildly in
order to show the effect. Your actual adjustments would not be this
extensive, but if your engine is loading up and not running very well, the
choke or an aspect of it's systems may be the culprit.
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)
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.
'77 Chevy K20: Quadrajet Choke Pull Off and Fast Idle Cam Observations
1977 Chevy K20. 350 crate engine. Rochester Quadrajet 4MV carburetor with
Truck suffers from unexplained hesitation and bogging when in forward
gears. Tends to rev just fine after a few minutes of mixed idling and high
revving. Checking choke operations as well as a possible sticky fast idle
cam as part of the process of elimination.
- Truck is allowed to idle/warm up until 2:25 mark, at which point the
engine is revved to about 2,000 rpm, and can be heard bogging (a hissing
sound can be heard). The fast idle cam is seen dropping. Fuel flow can be
seen in the glass-cased fuel filter right before the carb as remaining
- The engine is revved again about three more time up until 3:00 minute
mark. The engine revs slightly higher, but the hissing and bogging can
still be heard.
- Engine is revved again at the 3:35 mark, slightly past the 3,000 rpm
mark. Hesitation and hissing still evident, but less so than before.
- Engine revved at the 4:25 mark to about 4,000 rpm. No hesitation or
- Transmission is slowly shift through every gear starting at 4:55 mark.
Shifted back into Park at 5:05 mark.
- Engine revved again at 5:10 and 5:17 marks to 4,000 rpm. No hesitation or
hissing is heard.
To read up on the discussion, please visit the following thread:
Decoding a Rochester Quadrajet part 1: The name
Rochester Quadrajets tend to mystify people because of the various model
names assigned to them by GM.
Add to that a redesign in the '70s and the confusion only grows.
In this video we'll learn the different model names and also how to
differentiate between early and later-model Qjets. Enjoy!
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!