the question that isnt asked but should be is.... Do you break in your motors properly?? A fresh rebuilt 4 stroke motor needs to allow the parts to seat properly. You should never just rip on a freshly rebuilt 4 stroke unless you plan on rebuilding it after a couple of hours. I have run 4 strokes for over 20 years. I have rebuilt them many time and everytime I take my time to allow proper break in time. I have NEVER had a problem, and they last for a full season of racing. I always would burn a tank of fuel though my motors by running them at an easy pace. never any high speeds or high revs. Then i would change the oil after the first tank of fuel ran out. Next tank I would run the bike harder but trying to stay away from exessive overreving. By the 3rd tank you can let it rip. Four strokes can be a pain, but there are alot of moving parts in there with extremly high tolerences, these parts need to be seated properly or you will have a grenade every time.