I got a bargain on a few small universal motor that run on 120VAC and I'm trying to reverse the direction. I don't have a lot of experience with these types of motors but I do know they run on AC or DC and the direction can usually be reversed by simply swapping the wires on the brushes. On this particular motor swapping the wires to the brushes does reverse the direction but the RPM is slowed to about 1/3 of that in the forward direction. I have read that manufacturers sometimes tune the placement of the brushes to reduce inductive reactance but I'm not sure how to confirm if this is the case or what to do if it is. The schematic below shows my current test setup. I added a DPDT switch to be able to reverse the direction easily but my goal is to run it in reverse only. There are two small inductors on the outputs of the field windings just before the brushes but I assume these are just for tuning and would not be the cause of the issue but I could be wrong ( they appear to be identical on both sides but I have not measured them).
Is there anything I'm missing that would cause the motor to run slower in reverse or anything I can try to resolve the issue?