When I worked for a chain saw Mfg we never measured engine temps to adjust the saws. I suppose we could but after adjusting so many one learns whats the "best sound". Since I work in engineering if I wanted engine temps I would use a therma couple and a data logger to see what the temp was in flight. But I doubt thats necessary .. especially for Singles. A better tool would a Vibra tac. It operates much like a tuning fork except its a single wire. You lay it on your cowl and run your engine. When the wire vibrates at its widest point.. you take your reading and that's your RPM. You can tweak your plane using that.
Two cycle engines need the oil in the fuel to scavenge off the heat. If your too lean..ya loose power because of increased friction. If your really too lean you can toast your engine. If your too rich you loose some power but not the engine. Better to err on the side of a lil rich. Just my 2 cents.. BobH.