RE: OS .91 FX post-needle valve bubbles
Brad,
You should write to Bil Baxter (BAX) at the [link=http://www.rcuniverse.com/forum/forumid_133/tt.htm]OS Support forum[/link].
The older model .91FX had a heating problem, where heat from the engine would heat the metal needle assembly, which caused fuel to evaporate... Those are not air bubbles, but fuel vapors!
This could make your engine run terribly wrong!
It is rectified either by remotely mounting the needle valve assembly, or by the replacement of your current metal assembly with the new model's plastic assembly that does not transfer heat from the engine to the fuel.
I believe it is still done under warranty.