Have a 12.5 b&s motor in rider replac float/set needle in carb new filter also gas backs up into air filter and when I open gas shut off valve also leaking out of exhaust port/ any ideas what is going on? / Grass is getting longer

Hi,
Still some trash in carb or a compomised float, At any rate the inlet needle is not sealing the fuel inlet and causing this. You probably have the oil in the sump contaminated as well.
Peace,
Clarke