bored cylinder

hey i have a kx 125 bored to a 144 and im not sure if i HAVE to run race gas, i have heard you can run performance premix oil and just pump fuel and that will be enough, also if i do run pump gas will it only just not run as good or will the motor seize, any help would be apreciated

I presume you mean that the added bore raises the effective compression ratio.
2 strokes have relatively low effective compression ratios to start with
Try pump premium gas and listen for detonation. If you hear any try adding octane boost additive to the gas.

Also, it is important that your carb is jetted properly for your mods, riding and weather conditions. Also, proper spark plug heat range should be looked at which can help control detonation, if any.