A few years ago, I bought one of those little infra red temp checkers...just out of curiosity.
I tested several .40 to .60 size 2 strokes and remember that they operated best in a range from about 180 to around 250 degrees F. Once they got above that, perf. dropped off a bit, and 300 degrees was borderline too hot.

My measurements were taken as close to the glow plug as possable.

There is an emissivity setting that can be changed to allow for different surfaces...that setting can effect your readings.