New speed controller low torque. Works though.

[e bike journey]

I installed a new speed controller on my 12 inch 350 watt ebike and when I accelerate from a stop, the bike has trouble accelerating and the motor rumbles at low rpm, but once it reaches full rpms it's fine.

The original controller was 300 watts and the motor is an unknown angle the new controller is 350 watts and 60/120 angle

Just wondering what the problem might be with the ebike?