I recently purchased a 1990 420SEL with 208k. The car had a full history of every receipt from work done over the years. I love the car but it had one thing that annoyed me and that was a hard time starting. I replaced both fuel pumps, the accumulator and the filter. It started a little bit better but not perfect. I checked the fuel injectors and they appeared to be original. I replaced them and the problem went away. Now the problem was that it would bog down on WOT. I took it out for a drive and when flooring it, it would sputter a bit and then take off. I watched several videos and read tons of threads on similar issues so I adjusted the fuel distributor with the 3mm allen. In order for it to not bog down, it has to run rich. To the point that you can see exhaust and your eyes begin to water. I backed it down to lean it out and it bogs down again. I'm just trying to figure out if anyone has any experiences like this and what to look at next?

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Current fleet-
2015 BMW 750i xDrive
2009 BMW 535i xDrive
2004 Chevy Avalanche 4x4
1993 Mercedes 300SD
1993 Mercedes 300SE (parts car)

Previous Benz's-
2001 Mercedes SL500
1983 Mercedes 300SD
1980 Mercedes 300TD
1996 Mercedes E300D
1999 E300DT
1984 300TD-T
1988 Mercedes 560SEL (parts car)
1979 300SD
2003 E500
2004 S430 4Matic
2001 E55
2003 E430