BLDC Motor lurching with no load

Hello,

My motor is lurching/coughing/hiccuping (not sure of the exact term) at high RPMs, in which it will spin and then suddenly stop briefly before spinning again, causing the motor to 'jump' in its mount.

A few details about the set up:
Motor : Turnigy SK3 236kv (this model)
BLDC controller: 36V 500W (this is the pin out: gdocs link)
Batteries: 3 * 12V SLA battery

The motor is currently sensorless, although the controller has a learning function that technically allows it to work without hall sensors (controller is fine running without hall sensors).

I'm testing the motor at the moment without attaching it to the wheels so it sees no load, but it is lurching, and I cannot figure out why.

Any help is much appreciated.

It's losing synch when at high rpm. A common problem with many sensorless controllers. Not all, but some just can't handle the rpm, and lose snych. Stutters at high speed can tear a motor right off the bike, even some torque arms might not hold it down.

If possible, run with the sensors. Or, this problem may never appear on the road, where loaded speed is a lower rpm.