In 1968 Chrysler starts to use the Carter AVS carburetor. They incorporated a number of emission features within the carburetors. These are the features they incorporated;
Fortunately all of this can be corrected. However the corrections require the following;
- Sealed off the idle fuel mixture adjustment screws which means that you can't adjust the idle fuel mixture. By the way, if these needles aren't removed during cleaning then dirt and debris get caught in the circuit further reducing the idle fuel to the engine. And when this happens the carburetor runs leaner. Most people do not remove these when cleaning the carburetor because they are sealed off.
- Added an air bleed adjustment screw (most carburetors use 2 idle air bleed circuits, this screw added a third one), which means you can add more air to an already lean mixture.
- Used smaller idle fuel pickup orifices in the primary venturi clusters, which means you can only pull in so much fuel for idle. With todays gasoline you need more fuel at idle because of the alcohol-type additives in the gasoline.
- Incorporated a fixed idle air bypass circuit. This can be beneficial sometimes, but for the most part this circuit should be shut-off. My policy has always been deactivate this circuit first then reactivate it if needed. GM Quadrajets have this circuit also and I know this from my experience with Quadrajet carburetors.
- Added a clever device that introduces additional air when the throttle plates go off idle. However if you have to open the throttle plates more than normal to get the car to idle then you activate this device. And when this happens more air is added to the idle mixture. Also, as the carburetor gets older the spring looses its tension against the check ball that shuts off this device. When this happens the check ball opens up the passage and allows additional air into the idle circuit. More air means more leanness.
The write-up to correct this is lengthy. I can prepare this or I can discuss this with anyone who is interested. I can also make the modifications for you. I modified a 1968 AVS 4426S (383 manual transmission, I believe the 1968 383 Road Runner used this carburetor) and tested it on a carburetor flow-bench which worked fine.
- Thorough knowledge of the AVS idle and off idle circuity
- Special tools
- Special parts
I'm not trying to sell anybody anything. I've been doing carburetor restoration and repair for the past 15+ years. Most of my work has been with GM products. However I have a fondness for Chryslers (Dodge and Plymouth too).
If you have a question then please feel free to contact me. My name is Dan Squires and I can be contacted at
(630) 551-0595
[email protected]
Dan's Carburetor Service
Thank you very much for reading this.
