The wobble pump loses it prime and no matter how long you pump, it will not pull fuel from the tank on any tank selection.
I have the stock two line with the Y to the carb.
The owner complained the first wobble pump was weak and he wanted it changed. ordered an overhauled pump, installed, bleed system. it worked fine. He flew from Pearland Tx. to Sun and Fun Fla. and while he was there this problem came up. So, he ordered another wobble pump and an overhaul engine driven pump and had it installed there.He flew back to Pearland and everything was fine and then out of the blue the system kept losing its prime again and agian. I inspected the shut off valve and it was leaking really bad. Replaced it with an overhaul unit and replaced all the flex hoses and clamps. As I stated earlier, it will hold its prime and then just lose it and will not wobble up pressure. Have to prime system again and again. Any ideas???
Sounds like it is sucking air some point anywhere from the selector to the fuel unit.
Check connections in the wing/firewall behind the triangle panel in the R/H wheel well. Look for blue goo from fuel leakage. Check all connections along that feed line. You could also check the line condition by pulling the L/H stress door on the center wing section. There might be a splice with a rubber hose and hose clamps in there thats not stock. A hose connection could lose tension over the years.
While pumping the hand pump does any fuel spill from the carb?
Also I have pulled apart a new pump unit that had rust issues internally as there are steel plates inside. Also there are flapper units on hinges. Also a cast brass piece that rotates. It seals against the steel plates and has the flapper doors as part of assy. The unit rotates one way a distance than hits a stop, then reverses direction and stops. The flapper plates regulate fuel flow as the unit rotates. It basically alternates as an increasing chamber that fills with fuel and then dispenses the fuel as it reverses direction and the fuel is pushed out.
There is also some leather strips that act as a sealing device internally.
That is why a unit could have some corrosion growing internally, even if new or overhauled in the past, that could reduce it's sealing and ability to suck over time.