David,
I just find it curious that it didn't act up until you ran a modern engine. Glad to hear you have it worked out.
If you follow the setup and troubleshooting tips in the instruction manual you should be able to get the powermaster working.
Trying to run pulmor motors with it may require setting the stall voltage. That's starts the voltage up in the 5-7 volt range. The modern engines with electronic e-units don't need that much voltage to get going.