200° EGT differential

Variations in exhaust gas temperature (EGT) readings in the Rotax 912 engines can arise due to several factors. Some potential reasons for these differences include:

Cylinder-to-Cylinder Variability: Different cylinders in an engine might not receive the exact same air-fuel mixture, leading to variations in combustion efficiency and subsequently EGT readings.

Fuel Distribution: Uneven fuel distribution among cylinders can result from factors like variations in carburetor performance or differences in fuel flow. This can lead to dissimilar combustion temperatures and EGT levels.

Cooling Differences: Discrepancies in cylinder cooling can affect combustion temperatures and EGT values. Cylinders experiencing better cooling might exhibit lower EGTs.

Airflow Variations: Inconsistent airflow into individual cylinders due to factors like differences in air filter efficiency or intake design can lead to unequal combustion temperatures.

Calibration Issues: Sometimes, EGT sensors might not be perfectly calibrated or are "wearing out/failing", leading to readings that are not fully accurate.

If plugs are all good and gapped the same and carbs synced and mag check is good you may be on the right path to replace the offending probe.

Make sure that the thermocouple wiring connections are tight.  Thermocouple signals are in the millivolt range.  Connections that are not perfectly tight will cause a reading that is too low.  The error may be intermittent.

It will not be a calibration issue.  Thermocouple voltage signal characteristics are fixed, they depend on the Seebeck effect.  The calibration is set for the type of thermocouple but is not otherwise adjustable.

Another common reason for a difference in reading is that one probe tip is not making firm contact with the exhaust.  

I have fought this battle for years.  200 isnt terrible. First egt Probes do fail but mine seemed to be more random ups and downs when they failed. New probes don't seem to last as long as originals for some reason. Chinese junk possibly.  For some reason the factory installed my probes incorrectly, one on the front cylinder and the  other side on the rear . They are always off about 150.

I bought probes from westach.com and they seem to work better than others at half the price.

Thanks for all the replies, I appreciate the information.  Closing the loop on this topic, I pulled the offending egt probe and discovered that the tip was corroded/burned away, exposing the actual probe which is normally housed within the sealed metal sleeve.  This was undoubtedly the cause of the sudden and unexplained egt differential.  Will replace both probes, problem solved!