Hi Paul
Generally leaded fuel and rich conditions are the most likely to be a problem. Rich engines, normally carb versions, see the most. If equipped with carb heat and overuse of that feature can be a problem as well. Mogas is fine but again rich running can produce enough carbon to stick rings. The same issue comes up on engines that run the engine overpitched, mostly with fixed pitch, and never let the engines run up to good operational temperatures.
Fuel injection is a plus to avoid rich running and therefore less likely to get ring sticking. We know that the injection in ECO mode, your fuel saving mode, will allow the engine to run at lean of peak and that is a good thing.
Mogas has some great features however it is certainly not stable for any long term storage in your aircraft. Dont leave auto fuels sitting for more than a few months. If it sits then the lack of cleaners within the fuel allows fuels to varnish and this can plug up carb jets and even fuel injectors.
My tip for Mogas users, if you are going to put an aircraft into storage of say more than a few months, fill up with some Avgas and run it to where its circulated into the whole fuel system. Avgas has about 20% toluene and this keeps all the fuel system nice and shiney, no varnish. (change the oil and filter at the same time, old oil has lots of contaminants and thats not good for storage)
Cheers
