2004 Renault Clio Coughs and splutters when it feels like i

it seems to have an over fuling problem as is coughs out black smoke but it only does it sometimes mainly on cold days whether the engine is hot or cold i have changed the coil pack cleaned the plugs cleaned the fule system i know the fule filter has never been changed as you have to remove the petrol tank to change it when it happens the car judders and the power dissapears the more you try and accelerate the worse it gets it only seems to do it bellow 3500 rpm and 70mphand ideas would be greatly appreciated.