Ceke - hello how can the Webra 40 throw a 12x4? That is totally off la ... you want something like a 10x6 for a 40 sized engine, you may also go for the 11x5. Not a 12x4 la, that is why you are getting 10K RPM, you wanna prop her to about 13K, its a 2C engine and not 4C. ALso, fly the SuperChipmunk la of not send it back to me please!!!