Why does my Holly NH carburator still leak?? New float , new needle seat . Runs great then engine quits and fuel flows out of the carb intake.
Before installing the new float valve, did you make sure the hole was clean? A bit of debris or a piece of old gasket can keep the new gasket from seating properly.
Remove the needle and seat. Find or make a wooden dowel that will JUST FIT in the hole the seat came out of. Chuck it in your drill. Coat the end of the dowel with grinding compound. Stick the dowel in the hole and run it at high speed. Repeat until the seat where the gasket fits is shiny and smooth. Put the seat back in and tighten it tight. That will stop about 90% of leaks if you have already checked the obvious things like the float not sticking, the needle actually working, etc.