I bought a YS but broke the boom trying to slide the pieces on, so I ordered a new boom and haven't got to fly yet. Did you have this problem with yours? I sure don't want to go through that again. I sanded the spots like the addendum said but could only get the first piece where it needed to go then nuthin but problems with the second piece. Unless you got the addendum showing the new specs for the sanding spots your plane will be of cg. I know some have used this motor mount system
www.geocities.com/horseflyhobbies/ and most have also upgraded to more powerful engine. I got my plane from NorthEast Sailplanes in a combo deal and it came with Hitec RCD HS-55 servos and a NiMHd, 8 x 720mah, AAA (9.6v) battery. I guess they heard about all the performance problems folks had with the 6-cell 650mAh battery (7.2v) battery. I have read where lots have adjusted the thrust to about 3 degrees from the stock 6 degrees and get lots better performance. I have heard lots of great things about the YS once you get the CG and other problems fixed. Say it is a great flyer and getting 30-45 min. flights out of lipos. Some using it for AP and says like a new plane with larger or brushless motor on plane. Good luck!