Yor basic problem is that its is over fuelling in that 1 cylinder but it depends if you have injectors or a carburettor, to which your problem lays. if you hav a carb, and its only doing it in one cylinder then chances are you have i sticking valve or a worn valve seat somwhere. if however you have an injection system its most likely going to be a faulty injector or and ECU (electronic control unit) problem
Richard Warrington, February 2005