I run 10t pinion on my blade cp, I have used stock motor and stock tail motor and stock 4:1 etc, with sim blades all summer. You have to make sure your blades are in good shape, these helis don't have the extra power to work with less then perfect airflow.

Very important, are you slideing your idle adjustment up before flying. Again these need all the power you can get, conect your battery, wait for the green light then adjust the idle up until your tail starts to spin then back it off a click or two.

I don't mean to sound condensending, you may be more experienced then me and have tried all these, you didn't say if you are newbie or old pro with other helis.