May I suggest you view this video with regards to your H9 Spitfire?
http://www.youtube.com/watch?v=t-6pp...e=channel_page

Make sure you have the elevator joiner properly installed. Consider replacing the joiner with a stiffer piece of music wire.
Make sure your hinge gap is as tight as possible.

Consider using a dual pushrod to each half of the elevator.
Also think about stiffening the horizontal stabilizer with gussets or sheeting.
Try to avoid a straight down mounting of the cylinder head. I am just guessing that this particular plane may have had a unique vibration situation with the YS mounted with the cylinder pointed down and that this coupled with other possible contributing factors made the flutter fatal.

I know this is the YS engine forum. I run almost all YS four strokes on my planes.

The plane in the video was brand new with a new YS 1.10S in the nose.

Good luck.