214 won't be a far out for the the q128 , do you know the actual motor gear reduction ratio ?
Set the speed limit to 25km/h in the display and the correct wheel size then go for a ride with a gps , see if the two read outs match closely .
If the display over reads then try lowering the P1 value , if it under reads then raise the P1 value until both the display speed and gps pretty well match over a good distance .
Once one has the P1 worked out correctly and the speed reading close , one can set the display speed to read what you like