I want to pick up on something else here, that contributes to smooth running (core topic ) that firstly creates illusion, secondly to actively prevent giving a best course of actions in tackling uneven idle speed and hence promotes rattling.
The carburettor slides and their setting are not a solution for any cylinder to cylinder variable in how they are considered. The only thing they are changed for is themselves, they are categorically not in any way compensation for other issues that maybe in place. that's for all engines in reality.
The assumption, for that's what it is, that the setting of them via vac gauges hold technical authority over other methods is not correct. Reality is that it can, and does install an erroneous pseudo "parity" into them, that directly causes rough running .... while looking correct on the gauges.
I've written about this before, also it was discussed as to how Honda achieved this on production line too, when it was generally thought (by contribution on here) that they arrived to production with "bench sync" setup, which is vital in understanding this topic. Notably, they are very smooth when new, but have comments of never being the same again usually accepted from in service life.
I'll add more in next posting.
