Black smoke is the result of too much fuel for the amount of air available. This can be a result of several factors, either individual or combined. Dirty or plugged air filter/air intake passageways will cause black smoke from restricted airflow.
Worn fuel injectors that open at lower-than-designed pressure can cause Black smoke by allowing too much fuel into the engine for the air available.
A worn fuel pump can also cause this problem.
So can someone fooling with the pump adjustment on the back of the fuel pump. Turning this set screw just ½ turn can cause excesive smoking. I have never owned a diesel vehicle yet that SOMEONE didn't fool with this screw!
These engines were only rated for 58-62hp so balls are small anyway.
Fuel mileage won't be comparable to a VW diesel.
However, these engines are notorious for their longevity and reliability, if this means anything to you. My engine came from a truck showing 484,000 kms on the clock, and still going strong.
My opinion is, if you like the truck, spend the $ and fix it.
