I don't want to throw anyone under the bus, but when searching for anything similiar I found this.
viewtopic.php?f=7&t=6063&hilit=speedometer
I thought that maybe I was doing the same thing as that poster, but I am not. I have not yet rode with a gps to see how accurate the speedometer is, but in fifth gear at full throttle (I even tried to upshift to make sure I was in fifth gear), the needle tops out at betweek 50 and 55 (actually it hit 55 when I was going down a decent sized hill).
I am new to riding, and don't know much (anything) about engine, and don't know where to start. I'm just looking for some suggestions on where to start looking.