Question id 343 - Aircraft General Knowledge - Airframe, Systems, Powerplant - ATPL - Airline Transport Pilot license

Aircraft General Knowledge - Airframe, Systems, Powerplant - On the attached diagram showing the power output of a piston engine as a function of mixture richness, best economy is at the point marked:
3
2
4
1

Training tests and timed exam simulations ATPL - Airline Transport Pilot license