I have bench tested many different fuel pumps. The 216 and 235 and others use the same pump. I just bench tested a unit which was apart. I don't see how the pump arm will over stretch the diaphragm. My first guess would be tank blockage or fuel line. A full copper line would take 30 to 40 lbs. of pressure from the tank fitting. If you have an old soft line that is the likely spot because the inside rubber flakes' Doc.
