Simply the easiest and best upgrade for your GY6 150 scooter.
Use as an upgrade or when your weights due to being round have flat spots. This causes your CVt Variator to go the highest gear ratio as soon as throttle is applied. this cuases very slow take off and bogging problems.
An added 1500RPM Torque spring will make a complete upgrade. Do not forget your belt which is also work out of you have flat spots on your roller weights.
Your stock size is between 12 and 14grams on most GY6 150 engines. 10 -11gram is best for all.