Your problem could be caused by several things.
Most likely is a bad connection between the esc and motor. Could be a bad solder joint or a bad connector or a short inside the motor or a broken motor wire. All of them will cause your problem.
It could also be your trying to run a prop thats too big for that motor. It would help a lot if you knew which LS motor you had. Different LS motors need to run on very different sized props.
The "jet" motors are designed to run on very small props - in the 4" range - and the denovo series on some what larger props - 8" max on 3S. What size prop are you running on it now?
It could also be a setting in the controller. What settings are you using for PWM and timing?
Your motor will probably run best on low timing and 8khz PWM.
Do you know how many amps its pulling at full throttle?