The engish language manuals are available here in the states. EVERYTHING you'd ever want to know about this car, mechanically, can be found on paper or CD. The CD contains the Engine manual, body & chassis manuals, climate control and electrical troubleshooting. There's even a copy of the owner's manual.
This web site can sell you the CD.
If you email me (firstname.lastname@example.org), I can send you a .zip file that contains the carb adjustment data that I scanned from the introduction to service manual for this carb. Between a carb adjustment and setting the valve clearance correctly, you might make the car more peppy.
The smoke conditions you describe sound to me like there is some engine work in your future. Armed with the CD, a competent machinist and a parts supplier here in the states, you should have no serious troubles.
I have a 74 280C, which has the same engine as yours. I paid 50$ for a replacement carb in "good, used" condition.