RE: Enya 40 ss, leaning of when vertical
Trent,
...Did you try opening the main fuel needle more?
Make sure the fuel lines are as short as practically possible and that break-in has been completed as per [link=http://www.rcuniverse.com/forum/m_1850473/anchors_1850473/mpage_1/key_break%252Din%252Ctapered%252Dbore/anchor/tm.htm#1850473]this thread[/link] (ONLY if it is a tapered bore ABC/AAC, you did write 'piston and liner'...).
It must be adjusted by opening the main needle so the engine runs rich at full throttle, lifting the model nose straight up (have someone hold the model in this attitude), closing the needle to find the peak RPM and richening it 150 RPM.
If it cannot be made to run rich, or dies off despite of the rich initial condition, maybe the fuel pressure is insufficient.