It's definately priming with fuel.
Starting the Le Rhone is a relatively simple procedure ........ A person is needed to prime the engine through the exhaust ports or alternately swing the propeller in an attempt to “windmill” the engine to suck in the intake charge.
Nieuport 11 Bebe | The Vintage Aviator
The above link is most interesting, these guys build relica WWI aircraft, including the engines from scratch. The engine in the Fokker Dr.I was a German copy of the Le Rhône 9J, as used in the Sopwith Camel, though made of inferior materials. The Vintage Aviator group found various parts interchangable.
Richthofen's funeral.
Analysis by some has said that Brown was never in a position to be able to fire the fatal bullet on the trajectory found. As said previously, at no time did Brown ever claim that it was he who was responsible.