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You are supposed to adjust each screw, starting with #3 until the RPM no longer increases. Then you back it off by 50 RPM. Then adjust the idle control **** until you read 1,200 again. Then repeat for the other carbs.
The change in sound isnt severe no matter what you do. It's really important to have something sensitive to monitor it. I don't know if the induction tach you are using is accurate enough to do that. Like I said before I haven't used the one you have so I can't speak to it.