I'm sorry that it took a while to reply. I have been severely restricted in my internet access recently for two reasons. First is Bellsouth.net's ADSL line has been useless for anything other than small file email for a week now. They claim to be replacing a router or something.
The other factor is that I am writing an article (about MB A/C) for Babcox publication's trade magazine - "Import Car". I also spent the week-end in Ft.Myers at the yearly ASA convention (I am local chapter president and state board member).
The biggest problem is that I can't get to this site at work anymore. When I offered I never dreamed that the ADSL line would be still out yesterday when I went to work.
Based upon the further info about the D.C. Johnson box, I'm sure you have a simple K-jet system with an added frequency valve dropping control pressure. Follow the line from the center/top of the fuel distributor toward the control/warm-up regulator. The regulator is under the intake manifold on the block and is impossible to see from above but the frequency valve is usually right behind the fuel distributor.
I don't know how you will solve your emissions dilemma but for diagnostic purposes (bg) I would disconnect the electrical to the frequency valve (removal is not necessary unless its leaking) and readjust the mixture.
Once disconnected the mixture will be too lean if the system had been set up properly. If you have further questions about this email me as I won't see this if the ADSL link is still screwed-up but I will get my email at the shop. We installed about ten of the D.C. Johnson controllers in the mid eigthies on casrs we imported and federalized.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician