sons bike not shifting???

[freak]

I have a 96 lt 80.Motor seems to be strong just revs to the moon and only goes about 15mph.It dosent semm to be slipping just seems to be geared super low?Are they supposed to shift or this it???

[ss440ex]

Check your rollers in the front pulley,
under the left side cover.
Sound like its not shifting to a higher gear.