The use of carb heat as a check for to lean a mixture is the poor mans multi function mixture check and it is dependable...
If you find that you get no drop in power or an increase in power when you apply carb heat, that is a bullet proof indication the thing was to lean...hot air is less dense therefore hot air enrichens the mixture.
Normally you get a drop in power with carb heat due to the hot air enrichening the mixture.
So if the mixture is to lean carb heat will correct the to lean mixture back to normal...thus the increase in power..
Poor mans check and works every time to ensure you definately are not to lean.
See how nice I am sharing all these simple things with everyone.
Its usually the simple things that get us.
That and thinking with the wrong head.
Chuck