Re: New (old) stuff
The 48 is ridiculous. Out of the box it made an excellent rival in stock trim. But the Enfield bike it's on is significantly heavier than the bare bones Huffy. While I agree it should be able to rev higher, the 66 should come somewhat close.
I've seen that there are several differences between manufacturers. Some have very clean castings, some are ... worse. I had a kit once that the exhaust flange covered up 50% of the port area because the port was square and the flange inlet was a tiny round hole.
I know engines pretty well. I may not know every minor detail about the 66 and 48cc 2 stroke bike engines, but I've been around engines long enough to know that it's holding itself back.