There are more ways to avoid smoke in a non turbo engine:
- first, check your air filter or replace it, could be clogged.

-It's getting to much fuel:
turn down the idle fuel supply screw. Diesels are built to run rich on air.

- maybe injectors are worn out. Depending on mileage get them checked or replaced.

 

drive it

 

get it nice and hot from a decent amount of driving, and pull the airfilter off. start up the engine and get a spray bottle full of hot water. make sure it sprays in a decent mist. rev up the engine to about 3grand (almost full throttle) and spray a bunch of water in the intake while holding the throttle open. the water will steam in the combustion chambers and clean out a bunch or the crud thats built up in that old motor. repeat the bottle till empty a couple times and see how its doing, just make sure you leave it running for about 3-5mins after you finish spraying to make sure all the water is out of the system.

you can also try a diesel purge, that usually helps clean out old motors too.