Try loosening the gas cap when it starts shutting down. (IF the cap vent is plugged it will create a vacuum in the tank). How did you clean the carburetor out? You will need to use a carburetor cleaner spray, make sure you thoroughly clean any small passage ways. Make sure the little screen on the bottom of the pickup tube is clear. And I wouldn't take a chance with an old diaphragm and gasket...those frequently go bad and they're inexpensive, go ahead and replace that too. If it still makes trouble you'll probably just want to put a new carb on it. They're usually between $25 & $30.