Hi Polovski,
Yes, you could be right - if it was a late version of the Beardmore engine it would have had a mixture control lever
But Advance/Retard sounds like the spark (magneto) advance/retard to me - this was commonly found as a lever on the left hand side of the cockpit in German engine cockpit controls (and the Beardmore started out as an Austro-Daimler) where the throttle lever is on the control stick. The FE2b might have been different, but in most British and French controls I think the mixture control was usually next to the throttle on the throttle quadrant (and, interestingly, French movements were back to front, ie. move backwards to increase, forwards to decrease, if you want to model that correctly on French aircraft!).
Quick look on the internet and I found this picture of a spark advance/lever - not an aircraft one, but I think much the same!
https://www.themagnetoguys.co.uk/advance-and-retard.This is description of starting the 160 hp Beardmore from the Vintage Aviator, although I couldn't see a picture of the spark Advance/Retard lever mentioned:
The engine is relatively easy to start, in fact sometimes it starts itself ! After your engineer climbs up onto the wing root and carefully balances there while priming each of the six brass primer cups from a squirt can of raw fuel, he needs to clamber back to ground level and pull the engine through a few blades before the prime evaporates away. A call for “all switches off” signals the engineer that it is relatively safe to rotate the four bladed prop. Then, a call of “ready” from the engineer signals the pilot to make his last checks of all the cockpit controls and to ensure everything is in the proper position; fuel selector “Main tank to carb,” air selector “Hand Pump”, air pressure at 2.5 PSI, check service tank is full by looking at the glass sight gauge built into the side of the tank, position the spark advance to “retard” and now to try a start... Pilot calls “Clear” and selects “2” on the mag switch which allows the engine to run on both magnetos, then select “On” on the booster magneto switch, all this time the engineer is trapped in a maze of bracing wires and struts trying to remain clear of the soon to be rotating knives called a prop. If we are lucky the engine will come to life with just a spin of the booster mag, otherwise the engineer has to earn his keep and actually hand swing this very big, very awkward engine. Once started, maintain air pressure with the hand pump and keep the revs to below 800 RPM until the water temp reaches 60 Celsius. Move the spark advance lever to “Advance” and check for an increased smoothness in the engines’ beat. Before setting off it is a good idea to have your engineer look over the engine while it is running, as this aircraft is a pusher, there is no way of detecting oil, water or fuel leaks.
B.