It sounds to me as if the phase sequence might be incorrect, but it is worth first checking that the hall sensor plug is fully inserted into the socket and that none of the female pins
(?) have been pushed loose from the connector during fitting.
I'm wondering if the phase wire colours are in a different position on the MPIII compared to the Smart Pie.
If the way they are currently connected is wrong, there are five other possible ways to connect the phase wires to the controller.
Terminal: (1) (2) (3)
Option 1 B G Y (This should be the current position)
Option 2 B Y G
Option 3 G Y B
Option 4 G B Y
Option 5 Y G B <-- I would try this option first
Option 6 Y B GI know it's going to be time consuming to try all of the other options out, but I would start by swapping the wires on terminals 1 and 3 first so that they are in the same position as they were on the MPIII controller.
Only test with 1/4 to 1/2 throttle maximum at first, as using full throttle with an incorrect phase sequence can sometimes overload the controller's
MOSFETs.
The correct sequence should give a smooth running motor, if it sounds very harsh and struggles to turn the wheel, it is probably wrong.
To avoid any confusion, make sure you record each position that you try.
And don't forget to let us know which combination hopefully cures the problem.
Alan