Fuel problem '73 280SEL

[ggaz]

I recently removed the fuel tank from my 73 280sel 4.5 efi- Had it hot tanked & preasure tested, dried it out got it back in the vehicle within a week & put 5 gals. fresh gas in it. Car started but idled very rough. Did some minor tuning noted I couldn't get idle above 500 with idle mix screw-stopped engine. It would turn but not start again. Checked for spark. There is fuel getting to the ring but when return hose is disconnected after ring, I note that there is no fuel returning to the tank with ignition switched on and fuel pump (new) running.

I would appreciate any suggestions on how to proceed from here very much. Thank you.