I rebuilt the FD, didn't start, got a 560sel FD from junkyard, started but over rich white smoke, reinstalled SL500 FD, enriched adjustment 3 turns, runs great. The mechanic that had worked on the car before the previous owner gave up must have screwed it way out. BTW- The 560 FD plunger travel is 1/8 + more than the SL500. Changing the oil and making adjustments tomorrow. PO had champion resistor plugs in it, also one sparkplug wire was cut by a bracket in front. Also the best way to test for fuel delivery, bypass mas relay with fused wire, don't start engine, only turn on run for fuel pump to run, turn off, push down on air valve, watch fuel rise in fd ports. Should be even in all ports, no fuel = clogged port/screen, possible leaking o-ring?