Hi Marc! As you spend time here and read things I write, I hope you'll find your own answer, that I don't "hide things"....

the 91FX has done very well for us and we have had minimal problems. The carb on it is the same as on many engines for many years; that said, however, some modelers are finding that something is causing the o-ring at the base of hte needle to fail. For those that have this problem, a replacement needle seat is available.

In most cases, however, the problem is overpropping, based upon the Japanese recommendations in the manuals. They fly these engines VERY differently than we do, and their pattern plane prop range is just not fitting for the average US sport flier. The 13x8 is a GREAT choice and runs terrific for most users.