Rinojan PowerSpot

I have a mitsubishi delica l300 1987 g33b 1439cc carburetor petrol engine White smoke from exhaust some times when warmed up engine Failed eco test. They told me to adjust ideal jet. Report says ideal co2 emissions is high and rpm is 950 Mechanic says piston rings and valve seals are good I use water in radiator not coolant Anyone please can you explain me what is the problem?