I took a quick look at the .91FX manual. The suggested starting point for the mixture control needle is 2 1/2 turns out. Here's the text:
"Close the throttle rotor gradually from the fully opened position until it is just fully closed. (Do not turn further.) Then, screw in the Mixture Control Screw until it stops. Now unscrew the Mixture Control Screw as indicated below (2 1/2 turns for the .91FX) . See if this helps.