black smoke under load usually indicates overfueling(fuel rate set by inj.pump), or possibly air intake restriction,like a clogged air filter(mouse nest)-the engine fuel rate is set by pump but not enough air-/ so fuel ratio is off.If engine is all-gear drive design,you can rule out camshaft out of time if it's never been into before or if it ran fine before.Black smoke can also be indicative of an overcompensation of the governor under load
