YZ125

Primary compression is correct (stock). HGS Exhaust, VFORCE Reeds. Reed Valve Spacer. VHM Head (stock jetting).

410main jet at 25-30deg- 420,-440 below 25deg standard needle and settings clip 3or4 and std pilot. mixture air screw 1.5

Note. This 125cc engine is very well designed and makes very good power for a 125cc.engine. Be carefull of different exhausts and silencers as different lengh can effect flow and can result in bad piston detonation (destroying piston tops) Some exhausts dont pull enough heat from the piston crown. We have found the HGS controls the temperature very well ,as in Holland they race alot in sand. You can check temperature readings at the spark plug on the Dyno when testing on maximum run up and constant/steady load- rpm. Also its best to have the piston cryogen treated, using a different brand can be better, we use Vertex, they are a little heavier than the std piston, but seem to last .