Hi, have you tried looking at the camplate plunger? It`s a roughly 2" long tube coming out the bottom of the gearbox with a locknut. If you slacken the locknut and unscrew the plunger body, you can check the plunger and spring are free and not seized up. If all looks good put it back in and screw it in until you have a couple of threads left showing, or until the gearchange is not too stiff or loose. Bearing in mind, that if it`s too loose it`ll keep jumping out of gear, and if too tight, the gear change will be too notchy.
That`s the first thing i would check, hope that helps. Rich
