That motor looks like an early Smart Pie 3 like the one I reviewed
here.
As you say, it has been adapted to fit a front fork by machining off the threaded boss for the freewheel, and removing the cooling fan/disc mount. And presumably the axle has been reduced in length and the flat portions of the axle have been move in further by filing or machining them closer to the hub.
If you read my review linked above, you will see the following:
Also tested on 51.8V 14 cell 5Ah LiPo pack weighing 2.06 kg (4.54 lbs)
Maximum current: 31.72 Amps
Minimum Voltage: 51.98 Volts
Maximum Power: 1648.8 Watts
Maximum Speed: 25.3mph (measured with my phone's GPS)
The rpm of your wheel does not look like it would be anywhere near the 25mph that mine can do on a flat road.
Perhaps the throttle signal voltage is too low, or the Phase wire/Hall sensor wiring configuration is incorrect.
Check out
this post regarding the throttle signal voltage.
Perhaps the rpm has been restricted in the controller settings?
Are you able to access the programmable setting in the controller, if so, which software are you using.
(Smart Pie 3 uses different software to Smart Pie 4 and 5.)Although the Smart Pie is not very large motor, it should have more than enough power to pull away easily on the flat, but it will need some pedal assistance going up steep inclines, or the motor will struggle.
I have a front mounted Smart Pie 4 in a 27" wheel, and it will wheelspin very easily on loose ground when pulling away with full throttle, and I had to reduce the acceleration level to about 70% in the software to make it safer to use.
Alan