Usually the pilot jet is the problem since it had such a tiny orifice down through the center.
Open the mixture screw 1 turn to see if it changes.
Or a vacuum leak at the carb boots. Spray carb cleaner on the boot and see if it improves.
If that tamper plug is in, that is a screw for altitude, not emissions. You'll most likely need to see if the slow jet is clogged. Buy a can of gunk brand carb clean. See if you can spray cleaner thru the slow speed jet. With the nozzle that comes with the can, shoot that hole in the carb, or the most forward at the cylinder head side of the carb holes. Rather address it initially there first, then use a carb cleaning chemical added to the gas, and see if it will loosen up the possible varnish at the needle tip. If that slow jet was clogged, there is your idle coming back.
My suggestion is to never touch that screw behind door number two.
Go head make my day
Don't touch the idle mixture screw?
That is pretty hard not to do when the engine has changed and maybe the air filter and exhaust are no longer stock. Valves are carboned ,compression changes, carbs have leaky throttle shafts, timing chins wear, etc, etc.
I want mine to run the best and have good off idle response.