Craftsman Fuel Issue

Hey All,
Need advice!
 
I have a Craftsman 316.794400 31cc weed whipper that has started having fuel issues.  It stalls and lack of power when it runs but will idle. I have replaced all gaskets, diaphragm, and cleaned the carb. When I prime it, it seems to suck a lot of air through the supply line. The primer bulb is fine because I can pinch the supply line behind it and it stays depressed, releasing it inflates the bulb but draws minimal fuel. By accident I discovered that if I put my finger over the vent hole in the diaphragm cover plate and pump the bulb it will actually prime and fill with fuel like it should. If I keep pumping it will flood the carb. If I release my finger from the vent and prime again the bulb empties and sucks air again.  What are the possible causes?
 
TIA!