Lean or Rich?

[sizemic1]

I always forget..if an engine is running Lean, does this mean it's not getting enough air or not getting enough fuel?

[Nanotech9]

fuel... it runs lean on fuel and gets hotter and can burn up the pistons etc.

if its rich, its getting to much fuel, leaving carbon deposits on the plugs and pistons, running cooler, and may cough and sputter from time to time.

[bachviet]

You don't want to run lean especially in heavily modified cars.