Which is the correct screw to adjust idle?

[92470]

I should know this, but which is the correct screw to adjust your idle? I have a 71' Cheyenne with a stock 4bbl Quadrajet and the stock SB350. Right now, my idle is about 600 rpm parked and drops too much when A/C is turned on or put into gear. I would like to adjust the idle up to around 750, but can't remember which screw to turn. I hate to ask this, but a picture would be great as a reference for me. Thanks in advance!

P.S. does anone know what the factory spec. idle rpm is parked and in gear? Everything is stock, and I would like to have adjusted to what the factory specified, but can't find that. Thanks again.

[red69ss]

The carb throttle arm rests on the screw that adjusts the idle it should be easy to pick out pull throttle lever back and you should be able to tell which it is,I usually set it about 800 in park depending on cam

[jhow66]

Here:

[jhow66]

This may help also:

[Huck]

That's assuming you mean the idle speed adjustment---the idle mix adjustments are the two lower screws on the front. All this depends on good vacuum and correct timing adjustment!

[92470]

Both the photos really help. The one with the idle solenoid on the side has my curiosty. My carb has that on it, and I know it works and is hooked up correctly in regards to the vacuum lines. I am a stickler about originality and wanted it to operate as it should, but it never did in regards to the A/C

It will extend the plunger and up the idle at start up, and when I put it in reverse, like it should. But not when I turn the A/C on. I'm glad your post pictured that because I can't figure out why it doesn't activate the plunger forward with the A/C.

I also replaced the anti-dieseling solenoid under the dash with a NOS one. It stated clicking when I hooked it up until I screwed it to the dash so I know it operates, but again, would keep the clutch engaged after the engine is turned off like it should. I'm wondering if I'm missing wiring with these 2 related items.

Can anyone offer advice? Also, factory specs on idle at park and in gear? Thanks a bunch!

[jhow66]

Have never run across one with a anti-diesel solenoid under the dash. Explain how it is hooked up. Does the one on carb have a vacuum hose to it?

[92470]

It's under your dash on the bottom lip, to the right of your temperature control panel. It's a 3-prong switch that screws into the dash. I bought it to replace my original one from Classic Air Industries in Tampa. It was NOS still in the GM box and I think was labled, Anti-Dieseling switch. I'll pull it out and post the part number on it. I wish I could figure out why it doesn't work as it's supposed to. Purpose was to keep the A/C compressor clutch engaged for about 3 seconds after ignition is turned off to prevent truck running on, on dieseling.

[92470]

Forgot to answer you other question. Yes the true solenoid on the carb has vacuum running to it. If I knew how to post pictures on this site, I would snap one and post it. The solenoid on the carb bumps up idle via a extended plunger when ignition is turned on, when you put vehicle in reverse, and was supposed to when A/c compressor clutch engaged. Mine doesn't engage with A/C for some reason.

[jhow66]

I have assembly manuel for those years. If you will give me a few days, (wife is in hospital-knee replacement) I will see if I can find the details for you.

[92470]

I have the factory repair manual also, but can't seem to find out how the solenoid on the carb, the switch under the dash, and my compressor all connect together to bump up idle when A/C is turned on, and prevent dieseling when truck is turned off? Thanks for you help

P.S. hope your wifes knee replacement goes O.K. That's a bummer.

[jhow66]

This is an assembly manuel. Might be able to find something. Also has all the wiring diagrams.