I did exactly that and started with a CJ4 engine file, but it will not work.
After hours of experimenting, I noticed that the CJ4 file in the “SimpleAircraft” project works. I then changed the engine parameters to what I need and it still works.
Interestingly, when copying the flight model to the simple aircraft, the engines will not work anymore — strange 
Now I am changing the flight model parameters one by one and reloading the aircraft in between. A real pain in the ■■■, but I want to get to know which parameter is causing this behaviour.