Clean it. Make sure you run carb or brake cleaner through the air bleeds with the metering blocks off, pull out the bleeds if removable. Pull out jets and clean all emulsion bleeds including the kill bleeds, make sure all passages are not blocked. Also, make sure to use fresh gaskets making sure the bowl screws are tight. Loose screws will allow cross leaks. Blow everything out with compressed air before assembly. This is assuming the carb work correctly in the past.