Hi Denny, If you can feel (or hear when stationary) a light "click" when selecting gears, the detent plunger is enganging in the camplate slots and the gears should be in. If the gear still disengages, you could be slightly over-selecting, and going into a false neutral between the gears. I had the same last week from 1st to 2nd, and 2nd to 3rd. Stripping the gearbox cover revealed the selector stop plate tang for changing up (or down on British bikes
, i mean the forward tang to the right of the stop plate) had bent to the extent that it was touching the kickstart quadrant. After removal and bending back (by eye) so that the rear and forward tang where 90^degrees to the plate, everything now good. To set the stop plate, i also do this by eye so that the gearchange mechanism has equal movement between the tangs and comes to rest right in the middle of these. If the resting position varies, also check the return leaf springs in the complete assembly!