Short version of the long story is I have a tower .75 in my Bobcat and on the ground it reaches peak RPM but in the air it "acts" as though it has gone completely rich and won't reach peak RPM. Now I had a pet theory that positive air pressure on the exhaust is causing the muffler to overpressurize the fuel tank and you can read all about that here:

http://www.rcuniverse.com/forum/m_5103308/tm.htm

But Then I began to wonder about my prop selection. I have been running a 12x6P on this plane up till now. I did test run the 11x8P on the ground but it seemed to produce quite a bit less static thrust then the 12x6 so I used the 12x6.

The question is am I shooting myself in the foot with my prop selection. You guys have a great deal more hard earned experience than I have, please let fly your thoughts.