Hi Maxxie,
e i've made so far Welcome to the forum, the best bang for buck upgrade i've made so far, is Dr. Pulley sliders. Size for most KDU engines is 18x14 weight is specific to the engine, but for average 125, you should be close to 12.7 Grammes. Of course the next upgrade is good oil! Full synthetic 75-90W gear oil, and after running in, 5-40 synthetic engine oil.
Happy scooting,
Keith