Your KYMCO scooter has an automatic transmission, known as the CVT or Continuously Variable Transmission. Inside, behind the front belt pulley, is the “variator”, which has six metal cored plastic rollers that lay in a radial pattern nested in slanting ramps. These ramps allow the rollers to travel to the outside perimeter of the variator. The weight of these rollers is magnified by centrifugal force as the engine spins the pulley. The heavier they are, the further up the ramp they will roll.
As they move away from the center, the inner pulley half is forced inwards, causing the belt to ride higher in the pulley, increasing the gear ratio. Think of a mountain bike shifting automatically from the granny ring to the big ring… So, if you have lighter rollers, the belt stays closer to the center between the pulley halves as engine speed increases.
Lower ratios mean the engine is turning higher revs, which puts the engine in it’s power band, the rpm range where the most torque is produced, any time the scooter is being asked to accelerate. At cruise speeds everything should be as normal. Advantage is better acceleration. Disadvantage is slightly increased fuel consumption and engine wear.
Try this tutorial for what’s involved. I’m sure your mechanic will have fitted plenty of these kits and know exactly what to fit.