81 diesel rabbit (bad mileage - injector pump settings?)

[hackofalltrades]

The guy i bought this 81 rabbit from said he adjusted the injector pump (full load adjustment screw?) so he could blow smoke, (whyyy?)but he may have been just blowing smoke up my a**. I've been blowing black smoke as i accelerate from third fourth and fifth, especially in 5th on the highway, and i only get 31 mpg. I turned the adjustment screw down and the idle up and have been playing with that, plus i checked the timing and the pump timing was within tolerance at about .920mm. I went ahead and advanced it to 1mm. I haven't taken it out on the highway, or checked the milage yet, but i was wondering where to adjust that full load screw to with the idle screw to get it to optimal without the guess work. Also any other reasons my milage is so bad would be helpfull, thank you all, bye

[user removed]

Check the break off pressure of your injectors. Mercedes was something like 1800 PSI in the early 1980S. The spring in the injectors would get weak and the pressure would drop to less than 1500 and you would get clouds of black smoke and poor mileage. We found you could replace the spring and it would get the pressure back up to high specs, around 1800 PSI. You can shim the spring, but we found it was easier to just put new springs in the MB injectors and they were, in essence, "rebuilt".

regards
Mech

[DamageX]

Being able to blow smoke on old diesels with mechanical injection is normal. The injection pump doesn`t regulate the air/fuel ratio, you have to regulate it with your foot!

[drmiller100]

Originally Posted by Old Mechanic

Check the break off pressure of your injectors. Mercedes was something like 1800 PSI in the early 1980S. The spring in the injectors would get weak and the pressure would drop to less than 1500 and you would get clouds of black smoke and poor mileage. We found you could replace the spring and it would get the pressure back up to high specs, around 1800 PSI. You can shim the spring, but we found it was easier to just put new springs in the MB injectors and they were, in essence, "rebuilt".

regards
Mech

thank you. I wondered about how the old injectors really worked but have never taken one apart or played with one.

This is really good information.