Thanks Doc, did try clutch adjustment which was my first thought it didn't matter whether there was no free play still had the same problem, also tried the rocking back and forward without even realising it, looks like it might be that detent spring, but will wait and see what results from the change in oil.
It would not be a problem for me either but as this is young nephews first bike & he is learning the clutch/thottle gear concept, it will make it easier if he can select neutral. My boys experienced the same learning as you on your 400, however they were learning on a XL70 (no primary kick), they learnt quickly not to stall it.
Thanks for your help.