Primary slow mixture cut off valve?

[keruhas184]

I wonder if you guys have an idea on this one. After doing the complete vac removal and restoring the hot air pipe to get rid of carb freezing the car ran fine for about 500 miles (stable idle, etc). Now all of a sudden it can't hold the idle, and the only way it does is by adjusting the fast idle screw to 2500 - 3000 rpm. The idle constantly surges up and down, and if it goes below 2200 or so, stalls out.

Now, I think that the only thing left on the damn carb is the primary slow mixture cut off valve that could be malfunctioning and giving this problem. I guess i might also have a leak somewhere, ill try to look into that and will replace the intake mani gasket sometime soon. Pcv was just replaced with oem. The alternator is also brand (autozone) new. I'll check the mixture cut off valve per the manual tomorrow. But meanwhile, the question is, can this idle problem be anything else? Thanks.

[A20A1]

I don't think you mean fast idle... do you?

Do you mean the idle diaphragm screw?
Using the Idle controller/diaphragm screw to set the idle is causing the vacuum to drop, which causes the irratic idle since the idle controller is not supposed to hold the idle at that speed. It in a sense causes the problem it tries to fix... low vacuum raises idle idle lowers vacuum low vacuum raises idle idle lowers vacuum low vacuum raises idle.

Thats what that silly vacuum controlled idle diaphragm is doing.

https://www.3geez.com/forum/showthread.php?t=46572

that thread should help with idle adjustment, make sure you go thru the check list and look into other posibilities.

[keruhas184]

Um, my bad. I meant to say throttle stop screw. There is no idle diaphragm screw because there is no idle diaphragm. Its just a bare carb with all emissions removed.

[A20A1]

k, well that changes things.