Effect of unsynched carbs on rpm drop to idle time

Getting the basic stuff out of the way first is always the best.
Steve

Had the same thing happen to me maybe 5 years ago. Finally found that 1of the factory screws ( which had yellow Locktite on it) had backed off from the horizontal arm ( which has a groove it’s entire length) which connects all 4 carbs together. It allowed one carb to lag behind, so the return to idle was slow. Didn’t notice it on acceleration, that I remember.
Good luck
Joe