CB1100 Idle speed instability problem

[max]

Here's a thought; if the fuelcap is opened to release the vacuum, closed again and then the engine is started;
how long before the new underpressure has buildt up again?
In other words what role does the engine play in producing this?

Second test; run the engine with the fuelcap open and close the opening with your hand, can you feel the suction increasing?

Sorry dave, i am in guess land here since the evap rules are not part of my bike, but i hear what you say about it not happening previous to the iacv transplant and popgun's suggestion makes more sense than mine.