dude , buy a motor cycle if you want speed . its insane to try to get these bikes past 40 mph for a couple reasons, most MB'ers dont wear full face helmets and we all usually do not ride with leather protective gear , and a face plant at 40 mph is kinda hard on your body ya know.
These bikes are meant for easy cheap transportation at a fun and slower pace than a moped or motor cycle. enjoy them for what they are and quit thinking about land speed records. But if you do go for it , make a video I would love to see the accident waiting to happen video .
LOL good luck