If you add a piece onto the existing Spring, 1st make a tiny loop so when it pulls, it will hold, do that to both ends, then you could solder the two pieces together and get it to work. I've done this on a lot of lawn engines that have that same long spring set up. Kind of a hack, but works. The other way is to go to a really good hardware store, the really old kind, and search their spring inventory, I have found springs like that, sometimes too long, which is better than too short. A Kawasaki dealer may have something like that sitting around, especially an older one.