I have the OS.25 L.A in a GP .20 Cub. It is inverted and was a nightmare to get to idle . Went to a Fox glowplug with an idle bar and it improved the idle. Once broke in, it has been a very good engine. Sips fuel and the power was surprising turning 9x6 APC.
I got a new LA 40 with a trade and gave it to a friend who installed it on his Sig Kadet MKll . After a few tanks the engine has also been a great little engine. And no problems what so ever mounted upright.
Big Ed is right about the castor. I run Omega 15% in all my engines 80/20 blend .. The .25 has about 3 gal of fuel thru it , which is alot of flying considering it flies forever on 6 oz. fuel. And after 3 gals, it just seems to get better.