When trying to improve the performance of a "Pancake" motor one component to take a look at would be the motor magnets in the car. Having magnets of equal strength helps to maintain equal pull on the armature and therefore perpetuates electrical balance in the car. To do this you will need to determine the strength of each magnet. Enter stage right the One Stop Slot Shop (OS3) Magnet Matcher (MM).
First the OS3 magnet matcher is not a calibrated gauss meter. However, because you will be using the same measurement tool to measure the strength of your magnets it will allow you to match them by comparison. The Magnet Matcher is used in conjunction with a multi-meter. You can pick up a multi-meter most anywhere... however for ease of use I would recommend one with auto ranging capabilities.
The OS3 Magnet Matcher is pretty easy to use. The first thing is to turn your multi-meter on and set it to DC Volts. If you do not have an auto ranging meter set the meter to the 2 volt scale.
Make sure your multi meter leads are in the correct locations on your meter.
Insert the the red and black leads of the multi meter into the same color jacks on the magnet matcher.
Turn the magnet matcher on by turning the knob clockwise. Continue to turn the knob clockwise until the meter reads 0000.
Now place a magnet on the magnet matcher to get a reading for the magnet. Important Note: Be consistent where and how you place the magnets on the matcher. This consistency enables your measurement to be more consistent and accurate. The higher the number the stronger the magnet. A positive reading indicates a North Pole magnet while a negative reading indicates a South Pole magnet.
After measuring your magnets take a Sharpie marker and notate on the magnet the reading for that magnet. Then match the magnets up according to their measurement.
It's a nice little tool and as with any other tool the more you use it the better your results will be. Below is the instruction document that comes with the OS3 Magnet Matcher that you can download.