It starts innocently enough—in your fixed-pitch prop single, climbing out on a warm, but not hot, summer day, the VSI points to a number even lower than the usual lethargic rate. Or, on a cold morning the engine monitor on your Bonanza is showing higher than normal CHTs. Have you got a problem up front or is what you’re experiencing just a normal effect of changing temperature?
Your first action on the fixed-pitch prop bird is to lean the mixture because the most likely problem is that it’s too rich on this high density altitude day. Doing so improves things dramatically. The RPM increases, as does the rate of climb. However, you’ve pulled the mixture knob out more than half of its travel.