Most modern small prop propelled aircraft use fuel injection for fuel delivery, the mixture being controlled by a computer working in unison with the altimeter.
Prior to that they featured automatic, altitude compensating carbs.
But this is 1917 all mixture adjustment was the duty of the pilot, at any altitude above 5000 feet the oxygen content started to lessen, which meant the pilot had to lean out his mixture, if he didn't his engine would run rather poorly.
And he'd be prone to Stalling
Best you enable AUTO MIXTURE in Workshop . . . Let the computer handle this function . . . Later on you can deal with it . . . But that comes later
By the way, Von Richtofen was a great pilot, and an efficent Killer, but a great many of his early victories were slow British 2 Seaters 85mph flying in formation. While he had a Albatross DIII
The Red Baron stuff in his Fokker Triplane made great copy