G61/1 has tabs on it to prevent over-selection. I bought one, and had to bend both tabs back to get enough travel to engage gears. I have heard of people making their own version with adjustment screws to set the limit stops where they want them. I may have to do that myself.
Paul
The G6/1 can improve the gear change but due to the mix/match of components, they need some tweaking to have an effect. The standard G6/1 is quite flimsy. I made my own with two nuts for adjustment and some bracing to stop the nuts being bent backwards. A problem with this mod is that there is not much space here and the nut closest to the timing cover is fouled by the kick start mechanism. I have space as I have an electric start and the kick start mechanism removed.
This mod is only a partial solution as the G61/1 only limits the movement of the G59/AS. The rest of the mechanism inboard can carry on turning due to the momentum of the camplate etc. This is probably not so much of a factor for normal gear changing but more of a problem when going for a fast change or people who are used to stamping through the gears on more modern gear boxes..
Phil Irving proposed a fix by welding and filing to make a revised G43 that acts like more of a gear to keep it locked to the corresponding part on the G59/AS and so preventing the G40 shaft continuing to turn due to momentum. This is easier to understand with an M003 parts drawing to hand.
I think you may find it described fully in 40 Years On. I have not tried this yet, maybe sometime.