Greg, I have posted this question on the MB NSW Forum too.
Thanks for your reply.

This afternoon, I pulled the aircleaner and checked for vacuum leaks. All vacuum hoses are secure and not showing signs of deterioration. Fuel hoses look good too.
Pulled the spark plugs - all black - indicating excessively rich running. Couldn't find my Compression Gauge - last used in 1990 when I had a SI engine.
Looked ar dizzy. It is set fairly most of the way anticlockwise. Tried 5° clockwise, caused engine to slow down and lose power (retarded?). Reset to original position.
Still missing and backfiring thru inlet manifold at neutral throttle.
Car has a silver box marked Bosch, with wiring going to the engine near the FI system & Dizzy/coil. Is it spark control &/or FI control?
Would it cause this issue?

__________________
Tony from West Oz.
Fatmobile 3 84 300D 295kkm Silver grey/Blue int. 2 tank WVO - Recipient of TurboDesel engine.
Josephine '82 300D 390kkm White/Palamino int.
Elizabeth '81 280E, sporting a '79 300D engine.
Lucille '87 W124 300D non-turbo 6 cylinder OM603, Pearl Grey with light grey interior


Various parts cars including 280E, 230C & 300D in various states of disassembly.