Where is the carburetor idle adjustment screw on the Rochester ?

Right.

So by the logic of the diagram, you adjust the fast idle with the engine warmed up and the fast idle cam on the lowest step, I.E. - choke open.

 

Exactly - it makes no sense.

Once the fast idle cam drops to the first step, the only idle that can - and will - be adjusted is base/curb idle.

I blame the editors. They missed that section in 3 years of chassis manuals from what I've read.

 

The fast idle cam has steps that increase idle speed. You can move the cam by hand if you open the throttle a bit. Place it on the low step, and then adjust the idle with the fast idle screw to 620 RPM in Drive.

I find it easier to adjust the fast idle when the engine first starts to 14-1500 RPM. Play with the screw until you get that adjustment right. I made a video after installing my Electric choke. I had to play with the adjustment until I got it right. After starting it cold, the fast idle is approximately 1500 RPM. The fast idle cam rotates with the choke blade. The choke blade is opened by the primary vacuum choke unloader upon start up. I then step on the gas a bit, and the cam rotates to a lower step. The engine then idles at 1000-1100 RPM. I put the transmission in gear, and it idles dead cold in gear. Perfect.

 

Maybe I'm missing something here?

Once that fast idle cam is on the lowest step, doesn't that take the fast idle adjustment out of the equation?

Orrr...are we taking into account that the thermostat spring isn't fully constricted yet, thereby keeping the fast idle screw in play because the chassis manual states the engine should be warmed up.

 

The only purpose for the adjustment on the low step, is to get the RPM correct on the higher steps. I just make the adjustment on the high step. I think that is a better way, especially if you have modifications, and the engine, ignition timing, and carburetor jetting are no longer stock.

 

No, warm engine. It tells you that in the Chassis Manual.

https://www.v8buick.com/index.php?attachments/20221211_105319-jpg.592970/

I don't understand why this is such a big deal. Tweak the adjustment screw until you get a satisfactory fast idle speed when you start the engine cold. I aim for 14-1500 RPM.

 

OK, it is what it is, just do it my way and be done with it.

 

It makes zero sense.

How do you adjust the fast idle on a warmed up engine when the choke is completely open, the thermostat spring is fully constricted and the fast idle cam is dropped - due to gravity - to the lowest possible position it can be?

I'll stick with adjusting it cold.