I think I am a lucky guy, my only 91fx is flying on my dv (see above in the thread the building of this bird), this bird is now loging 500 flights aproximatly with the same 91 fx in the nose. The engine start at the first chicken stick hit and never stopped in flight, I never had to change any part of the engine.....
but i have to admit that before the first flight i performed a extensive carrefull breaking in of the engine.
the engine is still pulling my old dv in unlimited verticals.
I think the secret is in the fuel I use, home made mixture.....
Actualy I am very sick and don't have a lot of time to go to the field, I worked in the passed in a major european rc compagny as designer and test pilots, I have tons of birds home, but the dv is still my favorite


DV is my avatar on RCU, it's because the DV has been been design by one one of the best guy in the model world, I flown most of Bruce's design, they are simply perfect..... (Bruce shorten the nose of the the dv on the next batch, lol)