As delivered Rotax 912 and 912S don't have mixture control. The new ones do have a choke for starting rather than a primer.
The heads are water cooled and there are two (diametrically opposed ) CHT probe positions which enter the water jacket. One comes with probe in. My EGTs run about 40 to 60 deg apart but that could also be about leading and trailing exhaust positions as thay are in the airflow. That is pretty well the same amount as my friend's Cessna with injection so I don't think it is a function of carb/cyl. postion affecting mixture.
Yes, the manifolds are seperate (connected by balance tube app. 5mm dia.) and different length for front and back, (mine's backwards anyway) but that should not significantly affect MIXTURE. All the air passes over the same jets.
The mixture is self regulating depending on altitude, (some auto carbs used to do it too,) The only proper way to change the mixture for any given circumstances is to change the jets. Rotax recommend changing the jets for cold weather, ( ie for Winter here!) but most I know just adjust the idle up to about 1800 revs so it doesn't quit.
912 and 912S (and I think 914) are not supposed to need carb air warming. (According to Rotax that choice is down to aircraft manufacturer and they (Rotax) "are not responsible." ) However in some countries the regs say all planes must have carb air hot (Aus for one) and locals have mods to suit. The UK Rotax agents sell a throttle body warming jacket as an alternative. I have had my Rotax 912 quit on going to idle on landing on a 2deg C day with heavy humidity ( Low cloud lying in long strands down both sides of the valley and heavy condensation running like rain off all the metal rooves.) After being allowed to stand for a couple of minutes she ran fine. Experiment repeated twice with same result. I suspect there was icing enough to shut off idle air with butterfly closed but not to clog carb when butterfly open.
Most 912 and 912S run fine and have good reputation but there are a couple of things. 912S not certified and supplied after prop clutch was discontinued can be subject to gearbox vibration at about 70 hrs. The fix is an expensive installation of the clutch. You pay.
There are some advisories out about rockers and cracks in crankcases but they are "inspect, " not mandatory replacements.
I think some serial numbers had some component replacement ADs "at next inspection but I can't remember exactly what. Rotax have a fairly good reputation but their behaviour over the gearboxes has got a few people riled up. I was delivered my engine after the defect ( which they claim happens on only certain airplanes but rumours said up to a third of engines) was recognised but they declined to do anything about it. Go fly it and if it occurs you can pay for the repair. (Approx $700 US for the parts I think,) I was locked in as my plane is only designed to fly with Rotax. Personally I find that a disgusting way of doing business. Imagine a car manufacturer saying " We'll go on selling this car with a gearbox that has a very high chance of failing at 70 hrs and if it does you can pay for an upgrade to repair it."
One owner persuaded the local agents to install the pre- modification set up as a test fix for the problem and has done a good number of hours since without trouble but I don't know if any agents will offer it.
There have been some issues with cold starting kick back but Rotax have upgraged the starter and local agents offered a decent deal for a while, (Well I suppose $200 for an avaition starter, even a very small one, isn't bad.)
Some planes with exhaust above the engine get through exhausts at a famous rate but I think regular 'under' exhausts are fine.
There is a group site for Rotax flyers but it needs upgrading, It includes all the two stroke types. I'll try and get a web site set up as a front end in the next few weeks (Kids get back from Uni!) and hopefully it'll get a few more members. You can find it at Yahoo Groups under "Rotafly" Membership is open and free.
Sorry, More.
Rotax recommend not using Avgas with more than 10% Ethanol or alcahol additives, danger of seals being damaged. Better is Ethanol free. Shell do that here, local gas co offices will give you the breakdown.
Rotax recommend not more than 1/3rd use of Avgas (100LL) or not more than 1 fill in three. Avgas deposits carbon on important surfaces. They also recommend the use of a combined synthetic/mineral oil if you do use avgas. Pure sythetics don't mop up the carbon so effectively. Rotax engines are geared and motorbike type oils with shear additives are recommended though one local operator here (flying school) has had best results with Castrol Syntec.