Working on a 429 / AFB combo with some idle issues. I've sorted out my air leaks and rebuilt the carb. I have the AFB carb with two idle mixture screws and the large air bypass screw in the center. Carb has NO traditional idle screw. I've read up and believe I'm tuning correctly, but still have the need for a traditional idle screw. I've read that you can drill and tap the main body where the factory "dimple" is and add an idle screw but, for the life of me I can't see the dimple. Wondering if anyone out there has done this and can post up a pic. Appreciate it!
There should be an unused boss between the throttle lever and the acc. pump linkage. I haven't done it, but found this....as you probably did. There are two approaches to the idle adjustment... 1) retain the "throttle closed switch contact" bracket (on the passenger side) and adjust the idle there...this was the factory curb idle adjustment. 2) Drill and tap the boss for the conventional idle screw. Drill the boss perpendicular and near the center, but align the hole with the throttle bracket extension. The factory screw size is 10-32. This approach yields an idle adjustment screw like earlier TQs had. There is a "dimple" in the lower casting on the front drivers side (where the normal curb idle screw would be located). Drill through the dimple using a number 21 drill, and tap for a number 10 x 32 machine screw. Obtain a 10 x 32 machine screw and spring at the local hardware or auto parts store. Install the screw and spring. Screw the idle air screw all the way in, and then adjust the idle the conventional way. Sorry I can't be more help, other than a bump to the top for someone that will possibly know more.
Pontiac did use the controlled vacuum leak idle on some models, as did several other makes. Can be very useful if trying to dial in an engine with a large cam; provided the idle circuit is configured for the engine in question. Jon
It's on a 66 Caddy. Rebuilt the carb and its much better, but it will only idle if I have the mix screws all the backed out (6-8 turns). No air leaks anywhere.
You don't make it easy, do you? In 1966, Cadillac had two distinctly different classes of Carter AFB; California and non-California. Had you answered the question as to which AFB are you using, we would know, and the answer could be more concise. If non-California, the maximum setting on the idle mixture screws is 2 1/2 turns. To get a more finite adjustment (for smog-emission standards) the California AFB used a different taper on the mixture screws, and the maximum settings was about 4 1/2 turns. Anything more than 2 1/2 turns on the non-California carbs or 4 1/2 turns on the California carbs can actually cause the engine to be leaner, not richer, due to leakage past the threads. Typically, for the non-California carbs, an initial setting of 1 1/2 turns on the mixture screws and 1 1/2 turns on the air bleed screw would get you in the ball park. I have no specs on the air bleed screw for the California carb, but would guess at 3 turns on the idle mixture screws and 1 1/2 turns on the air bleed screw. And if you have a p-conversion in the distributor, would highly suggest replacing it with points and condenser to sort out the idle. Then if you are in love with electronics, go for it. About 50 percent of those calling us with idle issues fix the issue with points and condenser. All of the above is assuming you have an original Cadillac carburetor from 1966. Jon,
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