some other things to note, the HS50 was introduced in the 71/72 range, and was always the mid 70's "square" topped shroud. since that shroud had no place for the rivet on id tag, they installed a small tag that bolted to a sidecover bolt, basically like the tag that came with a tec longblock replacement engine. They are really hard to find, does not seem like the mini bike companies were utilizing them, and I dont they were used too much on equipment either for the first year or so, probably till they were more "proven". Seemed to be game on by about '75 though for snowblowers etc.. 10lbs lighter than an H50 and a whole lot smaller!