As with the gearbox Return spring, this kickstarter spring is commonly worn on Norton gearbox's - often identifiable by the kickstarter moving backwards by its own accord on takeoff from standstill.
As with the Return Spring, a good quality original used as the template to manufacture these, and it should fit both Upright and Laydown (pre AMC) gearbox'sAs always,
Fitting it is a relatively simple exercise - remove the pressed steel end cover on the kickstart shaft and prise out the old spring from where it locates vertically in the kickstart shaft - always wear safety glasses when doing this, although it should not fly off (in case it should break). Then slide off the old spring - but before removing you may want make a note where the old spring located into one of the 4 notch's placed radially around the steel sleeve that the kickstart shaft fits into.
To fit the new spring - you first need to ensure the kickstart shaft is turned as far clockwise as it can go - this signifies the kickstarter being at the top of its swing. Then fit the new spring trying to ensure you have the most tension as possible applied as possible, by placing the horizontal tang of the spring in the notch as far anti-clockwise as possible - so it is pushing the kickstarter shaft clockwise with some tension while static. By doing this, you know there will be as much 'return' to the kickstart shaft as possible in use. How you do this is personal choice, but it can be fiddly, I prefer to fit the vertical tang into the shaft first, and then try and prise the spring into the furhtermost of the 4 slots I can achieve . . . again always wear eyeglasses - as you should when doing anything with springs.