Gear selection problems

Hello everyone, I have just joined this forum and just fumbling my way round, not being very computer literate I struggle a bit with this sort of thing! Anyway to the point, which is a problem probably of my own making, I recently decided to fit an RGM 4 speed close ratio set to my 920 commando. I bought a geabox off ebay to use for this as my original box was ok and I had plans for. The reason for the change was that I use the bike for hillclimbs (tarmac) amongst other things and thought that this would be a good thing to do to improve my times. I used everything in the "new" box except the gears and fitted new bearings bushes etc (Mick Hemmings) At the same time I fitted a Maney belt drive. My problem is that when changing down to second and again to first often the gears will not select properly and in the case of first often not at all. When the bike is stationary gear selection up or down is not a problem (engine not running) and neutral can be found without a problem with engine running. In the back of my mind I am wondering if now that the gearbox is speeded up if this is contributing to my problem. Any ideas?

Could well be the ratchet spring, the one that locates the gearshift pawl.
Had this problem with a new one, shifted up alright, but now & again it would not shift down. They were being sold with the wrong bend on the long ends & wasn't letting the pawl go to it's proper position onto the ratchet.

I had lots of problems with springs, bushings and the pawl, all the slop added up to not working. Renewed all bits and shifts like a dream.

Silly question,... Is the return spring OK. ie... Returning every time.
AC.

Thanks for the input chaps, going to check operation of pawl spring and associated parts-again!