My friends and I all made very fast mopeds back in the late 70s/early 80s. What we did was drill out the ports as big as we could, bore out the intake manifold and carburetor as big as we could (although I put a YZ80 carb on my Negrini), put in the biggest jet we could get, cut the piston so it would clear the new larger port, remove the air filter, remove the exhaust pipe entirely (more on that later) and of course we changed the gearing to whatever sprockets we could find. You must remember that there were NO performance parts back then and I mean NONE. We worked with what we had. No kits, they were all 50cc. That is all we did. We did not even know that they had timing to adjust! I would adjust the points to start opening a hair earlier than tdc. Now about the pipe. After a while somebody started to make a chamber pipe called a Proto Pipe. It was a slip on but we used to cut the exhaust manifold about halfway under the engine and clamp it there so the chamber was upswept. It exited around the seat height and looked cool as hell. Now the moment you have all been waiting for. These were all verified numerous times. I had a Negrini. They are vastly underrated. The frame and suspension were vastly superior the the Maxi's. I was clocked at 58. My friend Howard had first gen one speed Newport. I clocked him at 65 more than once. My friend Richard's Maxi looked bone stock but exceeded 60. Another friend Dirty Donnie claimed 70 but was never verified. All told at least ten of us went 55-65 and we rode in packs and passed cars. Of course off the line they were slow with those gears but the power helped once you started moving. All of this is true.
This is why I do not understand why, with all of the performance parts available today, we have mopeds that have been tricked out not even reaching what we used to get to. Of course some are but with WAY more performance that we could only dream of.
PS I just picked up a clean 1978 Maxi 1,5 and am in the process of making it go as fast as I can get it to so you will probably see me around here. And I want to thank you all for the huge amount of information that you put up. It is very helpful!