Fuel problem '73 280SEL
 

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.

Fuel filter plugged, most likely if not changed with the new pump.

Otherwise, you are going to have to check for damage/clogging of the in tank screen -- this is the 24mm hex "bolt" in the bottom middle of the tank, and should have been removed when the tank was cleaned (not necessarily your fault!) since it has a brass screen.

I'd check, carefully, for fuel delivery -- with the fuel pump jumpered and running, you must get a liter of fuel in 30 sec at the return line. If not, you have a stoppage somewhere and you will have to find it. A smashed steel line, a bad rubber line acting as a one-way valve, etc. Very unlikely to be a bad pressure regulator, but that isn't impossible -- in that case, it will run WAY rich, as in black smoke pouring out the tailpipe from excess fuel pressure.

Peter

Why on earth did you hot tank it? Not only do MB tanks have special coatings to prevent rust, they have plastic parts at the bottom to do certain functions. I wonder how melted they are.

Peter