I have a Twinstar with a pair of OS 25 LA's. I also added E-Flite retracts (lots of extra work but boy does it look cool on those low passes)

Just wanted to touch on what Ed said intially
Don't let your buddies tweak your engines.
Don't let your buddies mess with your engines.
and finally NEVER let your buddies try and lean/richen out your engines.

Here is a video of the maiden.
http://www.youtube.com/watch?v=oN1b-Xrs9MY 

Thanks

John