Idle air screw O Ring

[brewsky]

Took the carb on my 66 ca77 apart for cleaning several months ago. Just got back to re-installing and noticed I am missing what appears to be a 2.8 mm o ring the parts diagram looks like is used on the idle air adjustment screw. Must have dissolved it in the carb cleaning machine!!
Can't tell where it goes from the diagram.
Possibilities:
1. between the head of the screw and the screw threads in the reduced radius space
2. between the spring and the beginning of the threads
3. between the spring and the carb
Any help would be appreciated.
By the way, it fired right up on the first crank after sitting 30 years with a full gas tank after carb cleaning and a new battery, oil, and points cleaning.
TIA

[onchiman]

Does your carb have a round shaped bowl (maybe rounded is a better word as it's not really round) or square? I'm not sure if your carb is the same as the one on my CA77 but mine doesn't have an o-ring on the mixture screw. There never was one. I was confused too because the schematic clearly shows one but on my carb the milling is such that an o-ring won't fit. It works just beautifully without it.

[brewsky]

Mine is the square type. You are right though, the Honda parts diagram clearly shows one and says it 2.8mm.
The carb repair kit shown on Retro Bikes site does not show it in the kit contents though???