If your Yz 450f is running great....(i.e. no problems, spark plug color is good), do you still change the plug out every x number of hours, or should I leave the plug in ??? I've put about 20 or 25 hours on this plug and I'm wondering if I should change it anyway. I primarily woods ride, with an occassional slow run on the local MX track. I never race.... let me know whether to change or just leave it in till I develop a problem. Thanx.