I agree with thevirginian however I am a devout YS lover and say if you are going to do some thing do it once and do it right. Go for the YS .63 S. Sweet engines youll have it on any 40 size 3D plane available for ever. Eaisily pulls as much as the Saito .82. if not more 1.5 hp as oposed to 1.6 on the YS and they weigh the same. As far as fuel delivery and throttle response goes they are unmatched. Others may say if this is you first 4 stroke then a YS isnt for you I dont agree there is enough customer support for this engine that a novice can operate it and its not as bad as people make them out to be. Theres one more set screw and 9 times out of 10 it doesnt have to be touched. Worst comes to worse call Dave Shadel @ YS performance and he can talk you through any issue. Anyway just MO. in either case 4 stroke all the way.