I have a 99 warrior that ive been having problems with. For 1 it wants to pop into neutral when i go to shift into 2nd from 1st. then when i down shift it wants to pop into neutral before going into 1st. its a pain to shift on even a little hill it doesnt want to find gears. The last time i rode it, it was even hard to engage into 1st from a start. then when i did engage it seemed to be a hard jerk as it went into 1st. i dont know what this could be. Any ideas? Clutch? Shifter forks? Transmission? I just changed the oil also. There were a few little metal shavings in my oil filter compartment

 

Metal in the oil is a bad sign that maybe the transmission is coming apart. about the only thing externally that it could be is your shifter linkage. Yamaha put that stupid shifter linkage on the warriors that wear out, causing lots of slop in the shifter arm. You could check that and make sure the splines are not stripped where the shifter linkage connects to the shift rod.