the pump psi was acceptable on the other one so it'd have to be OK on this one. either the float or a part of its linkage is hanging up in its travel range or one of the mini screws that bolt it in is loose (you woulda caught that by now) or the float is partly saturated or Murphys law several bad needle/seat assys in a row. As you know its just like the float assy in a toilet tank, pretty basic. EDIT another possibility is minute debris in the fuel holding the needle open on occaision