Not having the carbs all the way in manifolds often signals hard rubber from time and sitting. Why worker can't get them in to begin with. If so you still could easily have cracks in the rubber, as forcing them the rest of the way is often what cracks them (more). 95% of the cracks you will never see other than the effect.
I set all mine with mixture screws at exactly whatever turn I choose, that's no evidence at all that someone never touched them, in fact evidence they HAVE. You attempt to avoid setting the idle mixture screws while syncing, you move the screws on the links between carbs to sync. Sometimes you may have to possibly move the mixture screws but not always. If already set to best idle at the idle speed you are looking for then no need to touch them at all. Taking too long to do the sync can affect that as the engine will run richer the hotter it gets while idling with no air running over engine, I always throw a box fan on the motor when doing it.
At the low mileage this one has I would expect the idle circuits to be clogged in some fashion as they do it at the drop of a hat on these. The idle fuel feed restrictions are almost always clogged. '81 may or may not be screw-in pilots, the earlier ones are pressed in and much harder to guarantee clean as you cannot get to the air crossdrilled holes in the top of pilot without the jet pulled and in front of you. The actual fuel restriction can be cleaned with say the smallest string on a guitar, or E string, around .013" diameter, the hole size of the jet there (a #35 pilot).
Old aircut valves can leak to affect idle too.
Valve clearances affect all around running too and the vast majority of these never get them set right again, why you can buy one and knowing that get it running right to double your money in a few days. Screw the Honda OEM spec, look for .005" minimum or risk holding the valves open. For a fact these can burn valves set at .003" OEM recommended, the cams move around in the heads more than the clearance at valve when running and what you get for clearance is never a real world number. The cam hole can be up to .006" clearance, and the cams move around up/down due to that and the neighboring valve springs pushing them around in the big hole. Another reason to open the spec up is that unlike most engines these usually CLOSE UP gap with wear rather than get looser as most engines do. The valves are only nitrided and the seats commonly wear more than valve tips and opposite most other engines.