The key was the carb had been disassembled. It's quite common for people to err when fitting the diaphragm pin back into the metering fork. When they do carbs always drip because the pin on the diaphragm is sitting on top of the fork, lifting the metering needle all the time. Really hard to tune since they will be running filthy rich. You have to slide the diaphragm onto the fork, usually lifting one end of the diaphragm for sighting to assure proper installation. Then add the cover plate.