I have 3 different temp guns and they all read a different temperature. If you have smoke coming out all the way through the throttle range you should be safe. Good power with good smoke is your best indicator of a good tune. For the low range, you can make a few high speed passes to clear out the engine and, after bringing it to a stop, pinch the fuel line about an inch away from the carb. You should get around 4 to 5 seconds until the engine wants to die. If it takes longer, the low end is too rich. If it takes less, the low end is too lean.