Sometimes your ears just burn.
The point to the above statement is that the mixture on all US MBs since 1980 is controlled by the engine management system. If you make adjustments that are felt then the system is broken or overwhelmed. Early cars such as yours had to have a base point set (adjusted) so that the cars controller has equal ability to correct both rich and lean. This is an adjustment but it only can be measured as the cars mixture stays the same and it runs the same. If the mixture changes as it is adjusted then the electronic control system is out of range.
Later cars even set their base adaptation themselves.
Bosch Master, ASE Master, L1
33 years MB technician