"Too lean" what does that mean? When you use ayES USE EGT IN CONJUCTION WITH YOURn EGT, it's really apparent when you've gone too far, (too lean) the EGT temp goes down. Some people make the mistake of leaning the engine down when they see the EGT readings go down, thinking they're too rich. Problem is; if you get too lean, the engine starts detonating, and the EGT temps go down. It takes some getting used to. I've tried to explain to people; if, coming out of a particularly tight turn, if the EGT is reading lower than before in that turn, open the low-speed needle, same with the top end, only you use the high-speed needle.
Another good thing about the EGT; it reacts to changes in exhaust gas temperature much quicker than the CHT reacts to changes in head temps. It's not so much that the CHT is slow but that the temperature in the cylinder is slow to get to the top of the head.