At a recent contest, I was walking by a group of flyers and the phrase, "the needle is not a throttle, it's a mixture control...." fell upon my ears.
Hey! I've heard that before!
If the air density changes, the mixture changes, so you have to re-adjust the needle. Easily done, but now if you're low on power, turning the needle in makes the mixture leaner, equals even less oxygen than what you had, losing power, losing cooling, causing run-aways. How do you get power back if you don't have a throttle? How do you get the motor to run cooler?
Wait until a cooler day to fly.
Or.........CH3NO2! It's the O2 part that brings back the oxygen missing in the thin air. CH3, being some kind of hydrocarbon, burns well, the two together cool well...So now all you need do is figger how much to add....
I know we all know this, but I tend to forget, so maybe by writing it down here, I'll remember better. Or, maybe it's all wrong, you can't trust everything you read on the internet.

dg