I hate to hear that you had a problem with your YS 91. I am putting the same combo together now to take the place of my WM Fun 3D that had an OS 160 FX in it and I ran it out of fuel at about 15'. Couldn't recover. I will be watching to see if I have the same problem as you.
Where did you end up with as far as the CG. and how much throttle did you need to hover?