WADR to your mechanic, has he put a gauge on the system and checked the control pressure? This will take about 5 minutes and determine if this is the cause of your rich running. You can get a rebuilt unit from Phil or German Star for $199

Also, normally you have to adjust the mixture after installing a different FD, but I'm sure the tech knows this.

Lastly, you asked in another post about the coolant temp sensor. There is one at the back of the right head, but it only controls idle speed.

Good luck,

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe