I don't think there is a best there is compromise with everything RC and the engine is part of it, I just sold my last YS 140 L in favor of the OS 140 RX that I have now three of.......I personnally tought that the YS was to high maintenance......and the last two new engines that my friend purchase were not running well from the factory....now one can always send them back but...we don't pay 900.00 cdn for each engine.....to have the privilege to get the YS guy's to work on them for free....I must that mine run very well from the box, but I was in need of another and that sort of scare me, also note that by the time I put the dual plugs head from 3M and the 70 B carb the OS 140 RX the OS is pretty close to that price, so money was not the only factors.

Daniel D.