I have a bunch of US 60htz motors that I am using in NZ that is a 50 hertz configuration. I have run the 60 hertz motors on 50 hertz but they tend to overheat at 100% load (air compressors starting and running under full load, etc). My question is if I can change the start or the run capacitor to a more efficient mF for using 60htz motors on 50htz. Thanks.

 

If the start caps are switched out after start, there is no point changing them, you MAY see a slight improvement by increasing the capacity of the run caps.
Ensure you use AC motor run grade of cap.
Max.