Are fuel and air filters clean?
Fuel hoses in good condition?
Does the smoke smell like burning oil or poorly burned diesel?
Agreed, this is your biggest clue.
If smoke stinks of raw diesel, this suggests you may be getting air into the fuel hoses. Smoke is more likely to be white ish.
Check all hoses from tank to fuel pump are fresh, not hard or cracked.
Check fuel filter is securely screwed on, check o rings on fuel filter.
You can use clear hose to verify if there's air getting into the fuel. Heaps of threads here about this or stuttering, rough idle etc.
if smoke smells like burnt engine oil, and is blue, then it could be worn valve stem seals, or worn oil rings that expand and seal better once warmed up.
If smoke smells like diesel soot ( not raw diesel) and is black, you probably just have or combustion due to engine being cold. Lower compression could contribute to this. Or bad injectors injecting poorly attomised fuel.
Does cycling the glow plugs two or three times before starting make any difference ( get more residual heat into them before starting ).
