Greyfoxx, I was quite interested in your solution to the Yak 54 being too tail heavy.
How did it fly? Can you provide picture of your plane with prop out so far?
I also have the NP Yak 54 140. I have a Saito 125 in it. Just made maiden flight Sat 7-14. It flew very smooth and stable and we were impressed that it only took a slight down trim to fly straight and level. There were no surprises and landing was smooth and controlled.
Looks really good in the air.
One of my concerns was that the Saito 125 would be low on power for the plane. This seemed to be correct.
I had to add 3.25 lbs lead around the engine mounting block to get it to balance at 138 mm from LE.
The plane came out total weight, no fuel, 13.5 lbs.
My next steps to achieve more power is to lean out the somewhat new engine. Also to move the engine forward some.
I had no thought of going as extreme as you have done. I would have to use quite a thick spacer to put the engine out even 3/4" from the firewall.
I did not have the original engine mount.
If none of this works I am considering to put a gasoline engine in it. Something along a 38 or 40 CC.