I agree - temp guns should not be used to tune engines.

Once you get it running, run it normally for a while, maybe a few high speed passes. With the body ON, use your temp gun to spot check the temperature. Only check the temperature to make sure you're not exceeding the maximum operating temperature. Depending on ambient conditions (temp, barimetric pressure, altitude, etc), your engine temperature can vary significantly.

Tune based on smoke and performance. Make your tweeks between real runs, not sitting there idling or reving the engine with the wheels off the ground. Use the pinch test for the low speed needle, or if you notice it bogs on acceleration, lean out the low speed needle.

I tune for performance, then richen it out a bit to make the engine last longer. Then run the hell out of it, check the temp, if it's pushing the max limits (230-300 F, depending on engine), I richen it up a bit more. Make sure the body is on for the temp readings and you're running the car - you want to simulate the cooling effects of real running. If you run too rich your engine will be extremely cool and you'll be blazing through tanks and decreasing your plug life.

If you can't accelerate out of idle, even with a new plug, you probably have lost some compression.

Don't F with the mid range adjustment (it's the LSN seat) if you have one - just leave that at the stock setting.