Okay well then it's not broken like happens to so many initially.

Did you try this yet?

"On your idle ... it could be too high or when you hit the brake it closes the carb opening (which cuts the engine off).

Do this and see if it holds true?

1. Turn your car and transmitter on (do not start it)
2. With your transmitter open the throttle up all the way (flooring it)
3. Check that the carb opens all the way up
4. Let off throttle completely (as if it were idling)
PEEK INTO CARB OPENING
5. Hit brakes all the way
6. Does the carb opening get smaller? (when you hit the brakes)

If so, you need to adjust your idle so that it stops doing that, I believe you would need to turn the idle screw (under the carb) counter-clockwise just until it stops closing when you hit the brakes. Make small adjustments and re-check using the steps above."