I'm not sure MB still produces the manual you need. It would be: Service Manual Passenger cars starting 1968 Series 108, 109, 111, 113 Maintenance, Tuning, Unit Replacement.
Basically, if you had it you might get yourself in some deep trouble. I can't think of an area of MB repair less suitable for tinkering. If you have an injection problem your best hope is that you can find someone like me to straighten it out. That means someone who has adusted one of those pumps a hundred times or more.
If you really want to suffer look in the archives; I have written the basics in a rather long post. If you can't find it let me know.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician