Have 1975 450 SL with D-jet fuel injection
Has 120K miles and is mechanically sound.
Tagged as gross polluter in California due to excess fuel at higher engine speeds.
Mixture if fine at idle and passes smog test at up to 1500 RPM, fails past that. The faster it runs the richer it gets.
Have good mechanich who has verified correct fuel pressure and has made all available adjustments.
Have to pass smog test before I can drive it again. (Can't even sell it w/o certificate).

Mechanic is down to changing parts on a trial and error basis, and they are all expensive.

Would appreicate advice.

MAKE SURE THE AIR TEMP SENSOR IN THE AIR CLEANER IS PLUGGED IN.
CHECK THE VAC. HOSE FROM REAR OF MANIFOLD TO MAN. PRESS. SENSOR.
THE MAN. PRESSURE SENSORS HAVE A HABIT OF FILLING UP WITH OIL(FROM CONDENSED VAPORS.
ALSO CLEAN THE CONTACTS ON THE THROYYLE POS. SENSOR.
MF