falcon409,
(I forgot your name...). On looking at the FSX piston engine cfg I find the MOI's even worse. You didn't use the 'FSX' cfg & air in 'FS9', did you? Anyway, here is the fix.

(Before/Original):
empty_weight_pitch_MOI = 1400.0
empty_weight_roll_MOI = 1137.0
empty_weight_yaw_MOI = 2360.0
empty_weight_coupled_MOI= 0.0

(After/Tweaked):
empty_weight_pitch_MOI= 41400.000 //1400.0
empty_weight_roll_MOI= 21137.000 //1137.0
empty_weight_yaw_MOI= 82360.000 //2360.0
empty_weight_coupled_MOI= 0.0000

2 things tell me I did not 'adjust' or tweak this section. (1). the '=' sign has a SPACE after 'MOI' (I always correct this) and (2). the value ends in 'xxx.0' and I always correct this to 'xxx.000' (3 zeros, and NOT 1 or 6 zeros). This way I know I 'touched' that section. Always. So I did not tweak or change the values. Sliped by me. Senior moment. Oh, you can use the previous posted MOI's, as an increase to a value HIGHER is all that is required to fix. Not critical. But, too high MOI's make it handle 'heavy', that's all.
Chuck B
Napamule