1979 671 TI. Engine has about 700 hrs since major. Engine would always start well and never smoked. This past season I was seeing a little oil sheen coming from my exhaust after I shut down. A mechanic took a quick look and said that it appeared one of the injectors was out of adjustment and that I should have the engine tuned. This mechanic did not have the time available to work on it. I had another mechanic who was highly recommended and very experienced work on the engine(s). He said he found one or two possibly bad injectors and recommended replacing all while he was in there. After replacing all the injectors, engine ran well for a while. After about 15 hours of running, the engine started to smoke heavy at all speeds. The mechanic re-checked the engine and claimed that one of the new injectors was bad and replaced it. Now the engine constantly smokes at idle even after it is warmend up. The smoke appears to be black and is light but enough to be a nuisance to those around me. The smoke will tend to go away at higher RPM's. Any thoughts would be appreciated. Thanks