New Engine problems!

Last night I added a new super stock RZ engine I simply unsoldered the old and resoldered the new. Now it's all messed up. I give it throttle and it delays then keeps going after i let go it sometimes randomly goes reverse and sputters everywhere it very hard to control. It will now stop responding to throttle and i noticed the ESC is very hot. Any Idea what just happened? Maybe this engine is not compatible with my ESC? It says it's for 7.2 volts which I am using. I have no clue.....