Hi and
to the forum.
Assuming that you have the expected 52V battery instead of a 24V battery
(Charger is usually marked 58.8V) then I would start by checking the +5V output from the controller, as this could be preventing you from achieving the expected top speed if the voltage is too low.
The throttle output signal voltage needs to be at least 3.25V at full throttle to achieve maximum motor rpm, but the signal voltage could be much lower if the +5V supply to the throttle is also low.
If you have the 3 pin pedelec connector on the controller's wiring, you can easily measure the voltage between the pins connected to the Red and Black wires which should be between 4V and 5V, but if you don't have the 3 pin pedelec connector on your controller, you could measure the voltage of the +5V supply using a voltmeter connected between Battery Ground
(Black wire on main battery terminal) and pin 2 on the unused brake connector:
I strongly recommend that you you place a short piece of wire insulation on the end of the Positive meter probe
(or wrap some insulation or masking tape around it to make a tube) to prevent the probe from touching against adjacent pins while you are checking for the +5V supply, as
shorting the +5V and Ground pins with the meter probe could damage the controller's +5V output:
If the measured voltage is below 3.25V it is probably the controller itself that is faulty and causing the problem.
However, if the +5V is above 4V then the controller may well have been reprogrammed to a lower maximum rpm. If this is the case, you will need the appropriate USB programming cable, PI-800 software and a Windows PC or Laptop to adjust the rpm setting back up to 380 rpm on an MP4 or MP5 motor.
The Bluetooth dongle and App could also be used to adjust the controller settings, but only if your motor is an MP5.
Please note that the older MPIII requires a different USB programming cable and PD-282 software to set Speed scale to 100%.
If your motor emits a noticeable
pinging noise when under load it is likely to be an older MPIII, as all the MP4 and MP5 motors are fitted with Vector controllers which are much quieter in operation.
Alan 
