question about syncings carbs

When I take the caps off of the top of the carbs would it cause a vacuum leak through the slide? Do I have to make adjustments with the bike off ? I have the vm28 carbs

it can change the readings depending on how worn the carbs are, but its not really a vacuum leak, sync em with caps off and then check em again with caps on and see if/how much it changes
u can bench sync with bike off, ( and carbs off for that matter) but yes the bike has to be running to sync with gauges/manometer