Adjust your valves and try a 14 X 4 W apc first. If the engine is still poor (was never really snappy) then go for a YS 63. The 63 will put out as much power as the Sato 90 with the advantage of placing your tank on the CG. I have Satos and Ys's and prefer the YS due to power when you need it. The YS needs to be broken in per factory recommendations and cared for properly as any engine. I seldom toutch the needle except for summer/winter weather changes. Some guys at our field needle every flight and ususally never get it right. When its running good, leave it alone unless it askes for a change! Have heard Sato 70's can not be made to idle. I have several of them purchased cheap and tick over as good as any. Learn your engines wants, keep it happy and it will keep you happy. If you really want a great engine, go for the Sport Jett 50 or 60 and find out just how well a 2 stroke will run. Throttle response and idle are beyond belief, great power. My 35 kicks most 46 and 50s buts. Hope the 14 X 4 saves you the cost of a engine for a while longer. You are going to like the prop size. Gives you more control at hover and more thrust to jump out of trouble. By