A vehicle may stall when someone hits the brakes due to problems with the transmitter throttle trim, low speed needle, clutch spring, engine idle speed and brake linage. Some of the issues require part replacement and some require adjustments.
Adjustment issues with the transmitter throttle trim can cause stalling and readjustment usually fixes the problem. If the low speed needle is too rich, the vehicle may stall until someone adjusts it. In some cases, the engine idle speed is too low and to stop the stalling, someone should increase it. For the brake linkage, someone may need to center the throttle again to prevent stalling. If the clutch spring is the problem, someone may need to replace it along with the clutch shoes.