Thanks for the comments so far.  I realized I left the specifics out of my original post.  It is a GMS 47 using powermaster 15%.  I bought the engine new around 2001 and put a couple of good years on it in an extra.  It's been sitting for about 6 years.  I completely disassembled the engine yesterday and all internal parts appear immaculate and good compression. On the ground and test stand, it turns an APC 11x6 and 12x4 (over 12000 rpm at an off peak setting) just fine.  It has great mid range performance and smooth, quick transition at from any throttle position.  The issue comes up when I simulate hovering by holding the plane pointed up.  I've tried adjusting the HSN to avoid overlean at WOT.  When I begin playing with the throttle, it begins to bog down and die at around half to full throttle.  If I quickly level the plane, it smooths out immediately.  I followed the SPA3dT plans from the spadtothebone website.<div>
</div><div>Metallica: Donna huh?  I grew up in Brownsville.</div>