Hey Marc, you are right. They are not designed to do 45mph, but with a little work they certainly will do it.
In fact it is too darned easy. Kids around here are going wayyyy to fast on these bikes.
I actually only got to 44mph. If I had put a 40t sprocket would have done 45.
50mph is exponentially more hp but I have no doubt it is quite possible, especially with a shifter.
That was on the stock carb, a stock non-cat pipe, stock ignition, and stock 44t sprocket.
Basically just a ported cylinder and rechambered head.
These motors are simple and crude but easily expandable.
Quality control is lacking, but if you want to play Burt Munro, these motors will take you places.
As a learning tool, they are fantastic. The cheap parts are affordable or can be replaced with quality parts.
I'm not new to 2 strokes, I've 40 years experience. My usual ride is a KTM so I know a quality 2 stroke.
One year of buzzing away on these cheap heads and cylinders has taught me a lot.
Don't knock if you haven't tried or weren't successful. These motors have a lot to teach.
Don't miss the opportunity to learn.