Does fuel come out of the primer onto your hands when you pump itIJ If so your primer is not sealing tight when you put the bail on it. My l2 was doing the same thing. It would let air in over night but would not leak fuel.
I have fought similar problems on the old l2s that have the snap on filter. We replaced orings and add piece of cardboard between clamp and snap on filter. Check the check valves in hand pump and the check valve on return line coming out top of pump. Quickest and best fix I have found is go to diesel shop and get one of them universal clicking type inline fuel charge pump. Put in line between tank and snap on filter. Your problems will very likely be over