You can continuosly run the bike as much as your body especially your lower back and butt permits you to do so. Honda stunner is a air cooled bike so no matter how many kilometers you run the bike the cooling process will continuosly keep going. Air will continuosly flow over the cylinders keeping the cylinder temperatures from escalating to higher levels. However avoid running the bike at higher engine r.p.m for long period of time coz it will wear out your engine faster. Cruising at 60 to 65 kmph is fine for 125 cc bike anything above that will increase engine r.p.m and wear and tear of engine. Also make sure your bike is serviced well, keep your bike clean and before a long trip make sure to give extra attention to your engine cylinder fins, keep it as clean as possible.