[Craig yfs 200]

Hi all
Recently bought a a yz 250 not Shure of the year but it is the older say 99 shape with square rear fender not the pointy 1 if that makes sense, bike starts fine idles fine and runs grand when I give it full throttle but if I give it any less than full throttle it starts stuttering and feels like it's struggling to come into power band, anyone have any ideas? Thanks