I am using a very sweetly running LA46 with the OS needle valve and the FP/LA25 (.260"ish) venturi in my plane. 6oz plastic clunk tank on muffler pressure. 10/22 fuel or 15/22 fuel (the extra nitro is great at my elevation)
The 3 things which made a huge difference were:
-1- Secure engine mounting. *
-2- Sealed needle valve with fuel tubing. **
-3- TT 11x4.5 prop (magic prop) ***
*It originally had a K&B 40 so I had to re-do the brass inserts to perform the switcheroo. The maple beams were somewhat oil soaked, so the epoxy just didn't have the ability hold the insert adequately. During the first 20-30 flights or so, the engine run was decent but somewhat inconsistent. I had to re-torque the 4-40 screws several times and eventually the brass inserts started to spin in the maple. I decided to re-do the brass inserts again, and the maple splintered. !?@!&%#@!
At this point I performed battlefield surgery. I grabbed my flush cut saw and amputated the front of the plane to the first bulkhead. I then made up a 1/4" plywood firewall and installed a plastic RC mount ala the Imitation. This solid, secure mount fixed most of the run problems, which I attributed to possible fuel foaming. My plane is quite old, ~25+years old. It's not a beauty queen from many prior repairs in its previous life, so having the engine hanging out in breeze on an RC mount doesn't faze me at all. I really kinda dig it, actually. Function over form. Zero regrets.
**The next thing was to seal the needle valve with a small piece of fuel tubing, as I had a idea that there might be some air leaking around the threads. The sealed needle valve produced an immediate and dramatic improvement to the run quality. The engine run is now very stable and the needle is more responsive. Simple to change. Try it out.
*** After reading the endless positive accolades about TT props on LA46's, I bought some Thunder Tiger 11x4.5" props on ebay. I really didn't want them to be magic. But...yes, for me, they are magic. They really are. The engine just settles into nice, happy, fast 4 or wet 2 in the air and it runs awesome and totally consistent the whole flight. I launch around 10200'ish. Awesome, consistent, repeatable run.