I think you guys might have overlooked something in propeller selection.
Air is rapidly getting a lot thinner, and the correct propeller at sea level (where we modellers practically operate, and where we select propellers).
The correct prop at sea level will be way too small at high altitude.
So this setup should be heavily overproped by our conventional standards, to be operating well at altitude.
I think a big diameter, fine pitch propeller is best for this project.
Just look at any plane whos flying slowly and carving for efficiency and pulling power. (slow flyers, 3d planes, helicopter rotors..)
They are all big diameter, fine pitch.
The big diameter steep pitch stuff is for speed planes, and is typically used on hotliners.

Walbro carbs does not automatically adjust for altitude.
If you used a chainsaw in the mountains, don't forget your mixture adjustment screw, because if it ran well at home, it won't up in the high mountains.