My .02 worth...I've flown my 4*60 for over a year now (not continuously!), & it's pulled around by a Saito .91. Engine fired the 1st time I turned it over, & has NEVER quit in the air. Sounds like a farmer driving a John Deere around at our field; I love that 4 stroke sound! When other pilots have their 2 strokes in the air at the same time, I can't hear mine; it's that quiet. BTW, as light as the Saito is, the added weight of a 4 stroke helps out on a 4*60...I built mine light, & would have needed more lead up front with a 2 stroke; at least the Saito is useful ballast. Just MHO. -Daniel