Tao Tao Atm 50's lagging/straining uphill

[JB86]

Hi, I've got two Tao Tao Atm 50 scoots. one is red, one black. The red one is the faster of the two. the carb needle was adjusted to add more fuel by raising the clip up. It worked, and worked great. 40/45 on straight roads 30 uphill. 50 and more downhill.lol Scary fast sometimes. For whatever reason, it started lagging. Going 15 mph uphill and 30/35 straight roads and slowed down drastically. My black scooter, no adjustments made, even went faster than my red one. I'm wondering the cause of it. Any help would be greatly appreciated. Just not sure why it would go from ridiculous fast, to slower than factory settings.