I have a new XB-600 purchased directly from X-Treme about 6 weeks ago. Right out the of box, the max speed is 12 mph. If you put it up on the jack stand with no load, the speedometer shows 12 mph. I can even ride on level pavement (even with 2 people) and still get 12 mph.
The first thing X-Treme suggested was replacing the batteries. They told me the batteries I returned (the ones that originally came with the scooter) all tested either bad or very weak on the load tester. They sent me new batteries. In the meantime, the motor failed. They sent me a new motor. New motor works, but even with the new batteries I still get a max of 12 mph. The head lights are bright and the only difference I can see with the new batteries is that it accelerates slightly faster than it did with the original batteries, but still max speed of 12 mph. By the way, I did verify that the speedometer is accurate using a stopwatch and a 1 mile course.
I am waiting to hear back from X-Treme on what's next. I assume it will be the controller. So I am looking for any detailed tips or instructions from anyone who has removed and replaced the controller.
Also, has anyone else had this problem?