CEM isnt complex at all, its very simple especially coz of the bugs,British merlins esentially all you have to do is switch the fuel on magnetos on ie press 3 keys, fine pitch, play with the mix by all means but its bugged and is meaningless at the moment, open your rad start engine, wait till its warm and off you go. simple.
Once up throttle back to about 2600 revs or so, close your rads a bit and use your prop pitch to regulate revs . You will notice that as you change pitch the revs and boost alter accordingly, just stay inside the limits you will be ok. if your revs start to get bogged down make pitch finer, if revs get to high courser pitch required. Dont worry about mix its buggered and needs fixing. Just remember these engines are very delicate, an extra 200 revs can kill them easy this is over modelled and is probabily there to stop people flying at engine limits all the time. a real life engine would probably have to last 50 hrs between services ( history bods will correct me im only guessing) in pc world we get a new one every flight.
CEM is worth doing, Its a satisfying aspect of the game to be burbling along well within limits with a nicely trimmed aircraft, it makes the scenery look a bit better. In fact after a while you will find yourself gazing at all those other switches in the cockpit and wishing you could use them all, you will want to have to give the primer pumps a few squirts to start up the engine,you will wish the bloody radio worked properly and most of all you will never enable the autopilot.