Gas pouring out of carb

I had a spare Carter carb that I switched out the Holley with and the problem followed. So i knew it wasn't the carb.
So, a friend of mine who is a mechanic said he had actually had situations where somehow there was a blockage in the fuel return off of the pump that caused the fuel to back up in the carb. So I took the return line off the pump and blew some air into it (listening at the tank with gas cap off. It didn't appear to be blocked, although the shot of air may have dislodged it. So I went ahead and replaced the fuel pump and my problem was gone. I will never know if the fuel pump was the problem or if there was something that got lodged and broke free after I blew air into it. But she's driving fine now.