I would be suspect of either a major vacum leak or a very rich mixture-run the engine and spray some carb cleaner or WD-40 around the gasket areas that you disturbed….if the engine changes tone or speeds up there is a starting point………..not sure if this procedure is as accurate as it is on a four stroke but I have let the engine idle then choked the intake with my hand-if the engine smooths out again suspect a vacum leak-weak battery could cause your issue also-white smoke would indicate a very rich mixture-is a gasket possibly torn or wrinkled allowing a full rich run condition-just my 2 cents but that is the direction I would hunt I have seen rotax service manuals on the web-check Scott Umbrights web site I think he has a link:cheers: