With the 4 stokes there is less difference in good running and bad than 2 strokes. I would rate 4S as this YS, Saito and OS equal with different targets,Thunder Tiger, Magnum. They all seem to run good, different power outputs but run good. 2Ss The best engine is the one that keeps running. OS on average is the best but the Chinese production has taken over with great prices but hit or miss quality. The carbs take a hit more than the other parts because the care needed in making them good is not there. ThunderTiger Magnum,SuperTiger are the better "not OS" engines and the GMS/Tower, SK and other upstarts are on the same level of hit and miss. I would say all the brands mentioned are about 90% of all engines run with the K&B, Fox,Rossi,irvine and others as fringe.