Its probably because your pumping more fuel into the carb then it can handle and thus the reason for it “pissing out”.  This can be fixed by doing the pump around mod or you can bleed off some feed pressure by adding a T fitting in the the feed line and then plumb that feed line back into the return line.  The easiest method would be to add a T fitting and bleed off some pressure, it will be the cheapest and fastest and it might work but results may very on it.

Depending on the pump you have it can be different.  I have the round Dellotro fuel pump and it has has one inlet and to outlets and a pulse hook up.  I plumb both outlets into one line and then add a T fitting into the single line before the carb.  One line goes to the carb and the other I send back to the tank as a return to bleed off some pressure from the pump so the bowl is not over filled.  I also have a breather line coming off the carb that I run to a catch can in case the bowl is over filled.  This works for my engine setup, it may not work for yours but its easy to try and cheap to do.