Listen to Steve-he has been helping me with my rich mixture-see the related posts on this Vintage section of the board.
To re-emphasize, the thermostat is the FI thermostat which is the vertical housing on the back of the pump with two hose connections. I ordered a new thermostat (PN 001 203 95 75), figuring that after 30 years, I would give the old thermo a rest.
Also see Steve's response re: what to check first regarding rich mixture before adjusting the pump.
1971 280SL Tunis Beige Metallic
1971 280SL Tobacco Brown (13K miles)
1970 280SL Deep Red
1994 E320 Cabriolet
1999 E320 Wagon 4Matic
2002 LX 470
1992 Land Cruiser