This is a 3 speed with reverse, 125cc (Teen size ATV). It will go BACK & FORTH between Reverse, neutral & 1st Gear, but not above 1st gear.

As far as trouble shooting, I have removed the outside cover and looked at all of the parts inside. Nothing is bent or broken. After I reassembled it, I also adjusted the screw on the outside center of the cover ALL of the way CLOCKWISE and then in 1/4 turn increments, I adjusted it fully COUNTER-CLOCKWISE, trying to shift it after each 1/4 turn, with no success. This was all done while it was running, and in 1st gear. At one point the shifter "felt" like it was going to shift into 2nd gear because you could "feel" a "slip" in the torque when you pressed the shifter down to go to the next gear.

Thanks for ANY replies!!!!!