Anyhow, I think a performance exhaust is the first upgrade anyone should consider. I mean what the hell were those Yamaha engineers thinking when they designed the stock pipe.
"Hey Asahi, this qt50 project is kicking my ass. It's doing 34 mph now and US moped regulations require us to keep it under 30."
"Can you turn up the oil pump anymore?"
"I don't think so. It smokes like a chimney burning pine wood in the dead of winter as it is and four strokes with the slightest tail wind."
"Throw an S curve into that 24" long header, that should slow it down real nice."
"Ah yea, why didn't I think of that, the S curve in the header trick."
And that's why your qt50 is so damn slow.