pull the air filter off and look through the carb, when u apply full brakes do u see the carb close fully? if so then you need to open it up more so when you DO apply brakes it still stays open about 2 to 3 mm....it may stay just enough open when your servo is in the neutral position to keep it running but when u apply brakes it counteracts the throttle closing it....you may need to adjust your servo a bit after doing that