I have a 98 rm125 i put new plates and steels in not too long ago...and it doesn't seem to want to grab at all, also when i let the clutch out slowly it tends to die all of a sudden. I think it just needs a little adjusting
And when you replaced the "plates and steels" did you also mic the springs? Clutch springs wear out also. Now presuming the springs are okay, how much play is at the ball end of the clutch lever? That ball end should move no more than 1/8-1/4" total before engaging the clutch. If it has less play, then loosen it up, if it has too much play then tighten the clutch adjustment.
Major adjustments are done down at the case, finese adjustments are done at the handlebar adjuster.