i have a1991 yz 125 that wont shift. i was riding it like i usualy do and on mi way home from the pit i had it in 6th gear full pin for a short time and wen i was slowing down i notised i was getting harder to shift. i stoped and left it in first and checked for any visable damege. there was nothing so i started riding and couldent get it out of first. i have the shop manuel for the bike and it dosent tell me nothing, nether will the local shops. dose anybody have any idea what could of caused this???