Without knowing the car, he could've had a bunch of junk in his old fuel line that got pushed into the bowls. Tough to tell.
I had this happen with an Amazon carb I bought. It came from their fulfillment center and had obviously been used and returned, and sold as new. There was sediment in every orifice of that thing. I was always taught to disassemble new cylinder heads and carbs before using. It removes a variable.
