There are a lot of things to do for resolve this problem, well
1 the motor
Maybe brushes have not a good contact with the armature try to control spring presure and its head connection, ok?
Next check the siliconwires soldering on the head maybe aren't good, these should be show like silver, than the male connectors are good ?
2 battery : The wires that came out (if you use a stik pack)are without cut
From the battery to the esc also inside the plastic cap?
If you use an assembled pack, are the connectors solder correctly?chek the voltage 8.4volts
3 radio: If you have a digital radio reset all and put your ATV throttle and brake at max, then repeat the set up, check all the signals will be correct, at the end with your stick to the max the green led on your esc should be "on" if is not repeat the setup
if you have this Tamiya kit please to avoid a bad surprise put on a ball bearings kit befor use this motor and put on the lowest pinion, althogth will burning all your plastic gear case, ok?