I have a 78 express.
Part of the problem with making them faster is that they were really not designed to go faster.
This was also built while Jimmy Carter was presedent.
Do you really want to put your life in the hands of something that old going that fast.
28 MPH is good for that Scooter. Treat it nice. It's an old fella.
You wanna go fast, buy something designed to. The brakes and the tires will be more suited and you're less likely to get hurt as a result.