By diaphragm do you mean the atmospheric metering circuit or the pump? If the engine is flooding, the pump obviously works so it is not a blocked impulse port or pump issue. That leaves the likely culprit the atmospheric diaphragm. If you replaced it with a new, then the two most likely issues are that the gasket was put on the wrong side of the diaphragm or the diaphragm was put on reversed.
You can google and get an exploded view of the carb and check for proper installation. A gasket is needed between the metering diaphragm and the carb, otherwise, the tip of the diaphragm will hold the needle open and flood the engine. Also, the center tip of the diaphragm that contacts the rocker only works properly if the diaphragm has the correct side facing the rocker arm, otherwise it can flood the engine as the rivet side extends further than the correct tip side.
Hope this helps.
Manual is at
http://www.google.com/url?sa=t&rct=j...77161500,d.aWw