The bottom carb (at a minimum) has an issue. You definitely need to revisit the carbs. A proper cleaning and adjustment is called for. That means removal, complete disassembly (including jets and emulsion tube "nozzle"), and then a 4-hour bath in real carb dip (for all non-rubber bits), followed by a liberal blow-out with generic carb spray, and finally a careful reassembly, paying close attention to float height. No shortcuts here. If you aren't able to determine proper float valve operation, seek the assistance of a more knowledgeable mechanic.