My buggy won't move, stuttering motor...

[el tomaso]

As the title says my castle neu 1512 1800kv motor wont move, it just stutters and I don't want to push it. Its in a tekno D8 with 5s 3300mah 55C and MMPro. Worked ok before on same setup with 15t pinion. Then the stuttering started, then suddenly it worked, back and forth. I tried first to turn up starting power to high in the esc, knowing the batteries could take it, and it didn't help. Then I tried to put on a 12t pinion to make starting easier for the motor. Now it wont move. I tried different battery, checked for stones and made sure it turns smooth when pushed. No go. Then other RC's took my time. (I'm building a tricopter)

So obviously I will change back to 15t and low starting power. But it started to go bad even with that setup....

Any thoughts?

Thomas