Buy a temp gun, It'll be worth every penny. The temp should never read 250, 230 at the most if you want the engine to last.
Where in tarnation did you get this spec from? I've never seen anyone use a temp gun on an airplane, mostly because with a prop spinning between 11,000 and 13,000 RPM its darn near impossible to get a correct reading.
High speed needle settings vary as well depending on temperature, altitude, humidity, etc, but in my experience 2-2 1/2 turns is extremely rich. Most of my engines have ended up between 1 and 1-1/2 turns out. Your setting will be determined by starting the engine, warming it up, setting the needle to peak RPM and then richening it until you hear a slight drop (200-500 rpm if you're using a tachometer).
After a few tanks, you'll begin adjusting the low speed needle, and this is where you tell the difference between someone who knows how to tune and engine and someone that doesn't. Throttle transition is the real test you're looking for on the low speed, because that's the performance you're looking for. You can tell if you're close with pinch tests at low speed, but good transition and smooth, low idle are more sensitive, in my experience.
With the plane warmed up and the high speed needle set as previously described, bring the throttle down to your lowest reliable idle. Listen carefully for the next 30-60 seconds. Does the idle speed increase or decrease while your waiting? If it does, you're slightly off, but you can't really tell which direction yet. Punch the throttle to full. If the engine hesitates or burbles, then spins up to full throttle, you're low end is rich. If it hesitates and then dies, you're low end is probably a little lean. Make a SMALL adjustment to the low end (1/8 turn or less) and repeat this procedure, including resetting the high speed needle. If after 3-4 adjustments (1/2 turn total) you're not seeing any improvement, return to your original setting and go the other direction. Go a full turn if necessary this time, but again, if no improvement, return to the original setting. Keep working this way until you get a smooth transition, and a steady, low (2500 rpm or less) idle speed.
Brad