Too many people think that screws are there to be played with (any screw), and seeing as the idle circuit has very little to do with the running of the engine as long as things remain clean and un-obstructed, there should be very little reason to 'play' with them, but if you do, it could make it somewhat miserable for a nice idling power plant. Now if things get gummed up or dirty, then it's time to dig deeper, hence there is a screw and the cap can be removed. Note: if the carbs were cleaned and the screws were not removed and the circuit cleaned, then you just might be running into what you are presently experiencing.