I’m having a problem that stumps me. On my newest project, 1985 ATC250ES, also known as the Big Red. I rebuilt the carb with a kit from GH Atv. Soaked in carb cleaner for 7 days, blew out all passages with carb cleaner in a can then blew out with compressed air. Bike starts up first press of the button but after idling for 1-2 mins starts revving higher. I have installed a new uni filter, checked for air leaks around fittings. Does anyone have any suggestions?

This is the tank, it’s soaking in vinegar now. Hopefully I can salvage it.