32 ADFA carb adjustment

[VermontMatt]

I have a 32 ADFA on my '78 124, trying to get the adjustment right. Trying to follow the procedure outlined by Weber, I turned the idle mixture adjustment screw all the way in, before backing it out slowly to find the point at which the engine runs best. However, with the screw adjust all the way in, the engine still idles at about 900 rpm. I thought that with the mixture screw all the way in, the engine should stall Isn't that supposed to cut off all the fuel to the idle circuit?

[131]

If the idle speed screw is holding the butterfly open too far you can start drawing through the main circuit, so the idle circuit has less control. Adjust the mixture screw out then back off the idle speed to between 700 and 800, you should then have better control of idle speed via the mixture screw, you should be able to get it to run rough if you screw it out too far, or stall if you screw it in. If not you may have an air leak other issue.

[VermontMatt]

Yep, that did it!

It turned out that the choke fast idle screw was adjusted way too far in, so even when the idle adjustment screw was backed out to the point it wasn't touching anything, the choke fast idle still had the car idled up so high that fuel was coming in through the main circuit.

The fix was
1) back out the choke fast idle screw all the way, to get that out of the picture
2) Once I did that, now the main idle screw was once again touching the linkage, so I was able to back it out and bring the idle down to about 800 rpm
3) once the idle was down into the proper range, the only fuel coming in was through the idle circuit, so screwing the mixture screw in all the way stalled out the motor

Then I adjusted the mixture screw as per the standard instructions, tweaked the idle a half turn, and now she drives like a piece of Fine Italian Automotive Technology again.