I'm a beginner but heres my $.02 .
Run the engine at half throttle with the plane level. Slowly tip the nose up vertical and listen for any change. just to see verify if its leaning out.
I don't know much about the plane you got but try sticking a 4 oz. tank in it and making a couple of quick flights. The amount of space your pressure line has to fill will be different. If you get any change with this youll know it not the motor ..if ya don't ya know it is.
That just a quick test for the fuel supply system.

Good luck