1972 CB350K4 Won't Idle

Attached pics are of left carb bits. In first picture, what is the brass(?) circle on the right? Second pic shows two tubes with holes, which reside under (above?) the 68 and 115 jets. These are emulsifier tubes? Is the threaded tube on the right, marked with "38", the pilot Jet? Is the Air Jet any of these three or is it something else?

BTW, I had bought a rebuild kit including the press fit tubes with the holes in them (emulsifier tubes?) and installed the new tubes. When I took the carb apart tonight, both tubes (the replacements) practically fell out on their own. But I remember pressing them in required a bit of effort. So I tried the old tubes again and they seem to have a much tighter fit. Is the tighter fit critical or do the jets hold the tubes in place?

Third pic shows the primary and secondary jets' sizes - 68 and 115 respectively. The manual (copyright 1971) calls for 60 and 115. The bike is a 1972, but could larger primary create any issues?

To jd50i, in fourth pic of the butterfly are the felt pads located close in next to the throat, or further out, nearer the spring and the nylon bushing? Is it easy to disassemble the butterfly shaft or are there "hidden dangers"? (Tiny springs, easily broken plastic bits)

Thanks
John

The "FELT" Parts are on the ends of the Throttle shaft.
They are held in place on one side by a press in Cap retainer and on the other side sandwiched between the end of the shaft and the Plastic/Nylon bushing.

They get Greased or Oiled with a heavy weight gear oil.
Their purpose is to seal the ends of the throttle shaft to prevent an air leak from behind the throttle plates whcih is after all the fuel mixing occurs.
If they have been dried out due to soaking in cleaner (the cleaner basically washes them clean) the seal will be weak on non-existant.

You will need to remove the throttle shafts to re-oil them.
The flet seal don't actually have to be removed themselves but it is next to impossible to get a heavy weight oil into them without removing the shaft.
NOTE: If you do this you MUST have a JIS Screwdriver Set or you "WILL" ruin the heads on the screws that secure the thtottle shaft plates.
They LOOK like a philips head but they are NOT. They are Japaness Industrial Standard which has a VERY different angle to the cross tip.
A Phillips WILL strip the head of those small screws.

Also the ends were punched and expanded to prevent them from backing out and being swallowed by the intakes.
This is not something you will be able to duplicate and will cause you to need to WORK them back and forth while removing them or they will bind.
When replacing them use RED permanant Locktite.

Update: I have not removed the carbs yet to get at the felt pads, but temps finally got above freezing today. So rode the 350 around the neighborhood for about 20 minutes to see how it ran with the throttle cables readjusted. Both cylinders were firing. Engine runs strong above 2000 rpm, pulls nicely through all he gears. Throttle response seemed good. Idle is better but still an issue.

I let it idle for about five minutes before riding and it seemed good. Rode a bit, keeping the rpm between 1500 and 5000. When stopped, idle still dropped but not as quickly. I increased the idle speed on both carbs and it seemed to improve at about 1100 rpm. This seemed high so I reduced it to 900. After a few more minutes of brisk riding, pulled into my driveway to watch and listen. Idle speed dropped but then recovered, swinging between about 900 and 200 a couple of times based on the tach readings. It did this for about a minute before it stalled out.

What might be causing the idle swing and stall? The dried out felt pads? I'll try to get to them this week, but I'm wondering what else could be a root cause? And why does the idle speed need to be adjusted when the engine is hot? What is the correct idle speed? Thanks.

John