A little carbon doesn't hurt a thing.

Now not once did I ever say "recommended setting" The correct needle settings for ANY engine will be determined by altitude, climate conditions, propeller choice, and oil content. There is NO SUCH THING as a correct setting for all engine types. Anybody that believes so has got their head up somewhere it can be hard to locate.

Nor am I going to tell someone that their engine is too rich or too lean. The engine owner needs to learn how to make some determinations by him/herself, and not completey rely on someone else to do it for them. The basic understanding of rich and lean should be reasonably understood by the time someone moves up to a gasser. Glow or gas, rich or lean is the same. Only the adjustment process should need to be explained by this point.

BTW, if I change nothing else on an engine other than the oil mix, I can, will, and have fouled plugs, OFTEN! Sorry for one of you in particular, but I go with reality, not theory and published script. As I've stated before, I'm not an engineer or an architect that relys on what should work based upon long and tedious calculations, but a person that goes by what actually works in real world practice.

As a footnote, changing the oil ratio will often require that the needle settings be changed to reflect the higher or lower oil content. The amount of oil used will change the flashpoint of the mixture. We only have a very limited number of plug heat ranges that will work with our engines and still maintain a resistor value, so we have to work with what we have available. Those that are using an engine/plug combination that don't have a "resistor" counterpart have a much more limited choice.