Out of sync carbs make it run rough at idle and off idle when accelerating it'll often burp. All the bad stuff goes away with more rpms. To sync the carbs you attach a 4 vacuum gauge meter to each of the intakes and set #2,3 and 4 to #1 vacuum pressure.

Give the carbs a good cleaning -- it's possible you got something sticking internally. The last carbed bike I tinkered with was a 98 and they had butterflies. The slide you're talking about was attatched to a diaphragm and was lifted up by the vacuum created as the butterfly was opened.