For the first time recently I took my newly purchased 2008 Agility 125 on a street with a speed limit above 35 mph. The scooter quickly gets up to ~45 mph, but just as it hits 50 mph it begins to lurch / surge. This particularly happens at wide open throttle. Easing off of the throttle slightly stops the surging, but the scooter still doesn't seem to want to go over 50 mph. Downhill with the throttle just below wide open it'll reach 52 or 53, but that's about it. I weigh 175 lbs and it doesn't seem to make a difference if my wife (~120 lbs) and I are riding double. Scooter still quickly reaches ~45 mph and starts surging / lurching pretty much at 50 mph on the dot, which happens to be around where I'm at WOT.
Any ideas? I'd love to solve this so I can go at least 55 mph and keep up with traffic on my newly found large street.