Why does agriculture tractor appear dark smoke

Many users are concerned about the phenomenon that the agriculture tractor appear dark smoke.The reasons for this phenomenon are as follows:
(1) improper valve clearance adjustment valve sealing ring with a poor contact. Check valve clearance, valve springs and valve sealing ring belt.
(2) inadequate intake or intake pipe blockage. In order to find out the reason should check the following: air filter is clogged; intake manifold leaks; turbocharger damage.
(3) cylinder, piston ring assembly badly worn. When this occurs, piston rings, cylinder pressure drops, resulting combustion engine can not fully black smoke, and the engine power dropped dramatically, when severe load, the engine will automatically turn off. Replace worn parts.
(4) the supply of high-pressure pumps for each cylinder uneven or too large. Cause speed instability, intermittent black smoke, should be adjusted so that the balance or within the scope of regulations.
(5) injection too late and should adjust injection timing.
(6) If the injector working poor or damaged and should be removed for maintenance.