RE: engine tuning
The low idle screw is in the center of the throttle arm/carb barrel. Turn it 1/8 of a turn clockwise to lean it and try again. BUT, if it is rich coming off the high-end it's probably rich at the high-speed needle, too. Again: 1/8 turn clockwise and see if it helps.
Don't have a throttle delay set on the tx, by chance?