I have a ys 63fz.  Ran fine but with low power(as compared to my other one). Now it will start and run fine at low throttle and hi for a few minutes then it will just quit. New plug,changed regulator with one known to be ok. Went to factory sugested HI-LO needle and reg settings and started over. I have run these engines for some time and have been able to adust them fine. Tank is being pressureized. Replumbed with new toobing, amd checked tank for leaks.  Cant figure it out.