High idle setting.

[dmjlambert]

This is the tune up sticker for my 1969 CST/10 with 350 engine, Quadrajet, and TH400 automatic transmission. Is there a factory spec for high idle? I don't have the Quadrajet that came with it any more. I don't know if it had a high idle. The current Quadrajet is a model M4ME from 1985-86 and it definitely has a high idle setting.

[Alex V.]

High idle on my '85 GMC with a 454/Q-jet is 1,900 or 2,000, just as a comparison.

[Steeveedee]

You can dial that with the screw. All you need for high idle is that it doesn't die after you start it. If you want to drive right off after you start it, you might have to set the cold high idle higher than if you let it warm up a bit. That also depends on the ambient temperature. Maybe just play with it a bit until it works like you want, since it isn't the original carburetor, already.

[FirstOwner69]

The factory service manual for a 350 with Quadrajet specifies 2400 RPM for the fast idle setting.

[dmjlambert]

Oh, thanks. I completely forgot about the service manual, silly me. I have a PDF of it and want to get a paper copy.

[68 P.O.S.]

On my 72, with a 350 and TH350, the sticker on the inner fender says high idle is 1500 and curb idle is 600 in gear. 2400 is waaaaay high

[truckster]

Originally Posted by 68 P.O.S.

On my 72, with a 350 and TH350, the sticker on the inner fender says high idle is 1500 and curb idle is 600 in gear. 2400 is waaaaay high

Not if you want to make it to work without ever having to touch the accelerator.

[RichardJ]

I agree with 68 POS. 2400 is way, way too high. Not only is there no reason for it, cold thick oil puts an unnecessary strain on the distributor drive to the oil pump.
Somewhere around 1200, IMO is usually all that is necessary.
With the choke closed, the rich mixture would cause the plugs to foul at normal idle speed of 600. By increasing rpm to a higher idle when cold, the extra air lets the engine run smoother until the engine warms.

Choke opening and high idle rpm should be tailored more to your climate conditions than any book setting and only after timing, mixture and idle adjustment are done.

[dmjlambert]

I disconnected the electric wire from the choke to delay the warm up of the choke while I fool with it, and connected my timing light/tachometer. With the engine cold, I pumped the accelerator a couple times and started the engine. I adjusted the high idle to what sounded like a smooth run and nice speed for high idle. I looked at the tach and found it was at 1400.

It appears to have 3 steps of high idle that depend on the temperature. It stays on one step until I lightly press the gas, then it drops down to one of the lower steps or steps off of fast idle completely, depending on how warm the choke is. This is my interpretation of how it is working, I could be mistaken.

[Steeveedee]

Originally Posted by dmjlambert

I disconnected the electric wire from the choke to delay the warm up of the choke while I fool with it, and connected my timing light/tachometer. With the engine cold, I pumped the accelerator a couple times and started the engine. I adjusted the high idle to what sounded like a smooth run and nice speed for high idle. I looked at the tach and found it was at 1400.

It appears to have 3 steps of high idle that depend on the temperature. It stays on one step until I lightly press the gas, then it drops down to one of the lower steps or steps off of fast idle completely, depending on how warm the choke is. This is my interpretation of how it is working, I could be mistaken.

Nope. Looks like you got 'er working just right. Might need more adjustment for different weather, but probably not much.