If you have replaced the entire primer bulb/pump, there seem to be two generic possibilities remaining: an air lock downstream of the primer bulb/pump, or an air leak or liquid lock upstream of the primer bulb/pump. If there were a downstream air lock, the pump would be unable to pump out the air inside the bulb and replace it with fuel because there was nowhere for the air to go. You would probably know if that were happening because the bulb would become difficul to pump after a few strokes. If there were an upstream air leak, air would be getting into the fuel hose when you applied suction with the primer bulb/pump. An upstream liquid lock would be something like a sticky valve in that round device you are holding in the photo. You would need to check the fuel hose connections for leaks, and examine that strange round device, which might be a fuel pump. If one of its connections or its diaphragm leaks air, or its intake valve is a bit sticky, all may be explained. We'd need a proper diagram and explanation of that rather complex fuel system to be much more helpful, I think. My guess is a serviceman would replace the priming bulb/pump, and if that didn't fix it, replace the fuel pump (if that's what the round thing is). Most likely it would be one or the other, and he'd have fixed it within ten minutes.
