I think the exhaust is holding you back. 70cc BBK's still running OEM exhaust?, anyone running Tecnigas pipe?
What year is you S8? 2 strokes after about 2005 are heavily restricted for EPA rules and don't run as well as earlier engines. Same engine, still capable of running great, just needs a few more mods. I have 2005 People 50 2Tand runs 50mph with only mods: cdi destricted, 85 main jet, the OEM exhaust doesn't have any restrictions and works great. I think your S8 50 2T has the same engine, so should be able to go a lot faster IMO.
I am looking to buy a used 2013 S8 50 2T, so I am interested in your issues.