I have a 5 hp briggs and stratton engine. The engine would not start unless you dripped gas in the carburetor. I put a new diaphragm in, and it still will not run unless you drip the gas in. There is no trash or rust in the tank. Could it be the breather assembly? How do you tell if one is bad.

Don't think so.
Did you clean the carb while you had it off .