1998 Other Renault Models fuel usage

Engine Performance problem
1998 Other Renault Models 4 cyl Two Wheel Drive Manual master miles

van has engine recent rebuild and gearbox same, engine rebuilt as person befrore not change oil ans was like grease. Now van starts ok drives too but when press excelerator lots white smoke and seems choke itself with too much deisel, when gets up top speed drives ok but if slow down on bend and try to pick up speed seems slow do so taks while to get back up, if keeep elcellerator pressed and slow down in neutrl and then reengage gear, keeps power ok, hopinh can help me thank you