IMS = Idle Mixture Screw (PD carbs have such a screw)
The earlier Cb550 carbs just have an air screw.
Have you found an explanation for why the spark plug deposits are different among the cylinders?
If it was just a jetting issue, they would all be the same. And, I expect you will never solve the problem with just fuel metering adjustments.
What do you know of the history of the carbs? Is there a chance someone other than Honda was inside and meddling with them?
Some possibilities:
--Non-Honda internal parts. (What number is on the needle jet?)
--Altered internal parts. (Drilled/bent/corroded)
--Mains emulsion tube holes blocked gummed. (Many overlook this important cleaning, as it doesn't naturally fall out of the carb body when the main jet is removed. And, it must be driven out from the slide needle end.)
--Air jets dirty altered or missing. (There is one for the mains emulsion tube cavity and another for the Pilot circuit that the air screw regulates.)
-- Carb body passageways corroded and restricting flow.
--Bowl fuel levels aren't the same in each carb.
These are all details of carb function that are often overlooked in the rush to go riding.
Do understand that the idle settings must be slightly over-rich. This is necessary to have engine response to throttle twist. You can normally expect this aspect of operation to suffer when pods are installed. But, right now you have to figure out why all four carbs aren't delivering the same mixture ratios.
Cheers,
