I have an escort gti which i have had for just over two years and all of a sudden it started to back fire and lose power, does anybody have any ideas what it could be?

If it is a major problem i would like to change the engine for a 2ltr zetec would i be better getting alate spec black top or a early spec silver top and is it a hard swap? or maybe a st170 engine?

any help would be much appreciated.