st-st-stutter 99 R6 below 2000 rpm

Hey guys, a friends bike is running like ass. under 2000 rpm he says it stutters.. He also says there is a lack of power/stutter under 2000 that is a pain in the ass, i dunno what else to say about it.. The carbs cleaned/sych'd, valves checked, compression checked, plugs good, coils good all that shit.. when the bike is at idle the idle moves around a bit, its not steddy..When hes riding the bike it sounds as if the rpms are going up and down almost, but they arnt.. just doesn't sound right at idle or while in gear riding the bike.. The bike is stock, and has a stock pipe on it.. Where should we be looking next, any ideas would be great.:dundun: Thanks,