TwoStroker

You are correct!!
When i race Kart a few years ago i set up for 320F- 340F+o- but and the end of race the engine are near to 400F and many times we have to pop puf the carburetor into the turn for down the temperature

For the engine in RC are the same.Engine below 300F don't work good, is too cold.
About the infrared temp is very precise, but you have to take the temperature at the moment.
In 10 second of difference you can have a variation of until 40F

If you take a engine in the test stand and and run for five minutes for and put full throttle a make the measurement you can see easy 300F.

Dick about the Mac 10'S is McCullough and you running it with alcohol?