Dont know why you replaced cdi, weren't you getting a spark before that? are you now? if not then check generator, coil & leads for output & continuity, a multimeter is useful for this.If a carb suddenly starts 'playing up' as you put it, a piece of muck could have made its way into one of the jets. check the fuel tap/filter at the same time.
Chris P.Duck, November 2010