In my experience with PA38, leaning for climb usually isn't neccessary, since O-235 shows pretty good performance even at high altitudes - if I remember correctly, some 300ft/min climb with full throttle at 8000 feet on close-to-ISA day...
Before attempting leaning in climb you should consult Engine Performance chart in PA38 POH, since you should not lean if power setting could exceed 75% of engine's rated power...
As being previously said, PA38 doesn't allow for precise leaning LOP since the engine basically "dies" just a little leaner of peak. In my experience, the best way to lean it (considering fuel economy and engine health) is to find the peak (EGT/RPM) and then advance the mixture lever 0.5-1 cm forward.
Originally Posted by A and C
I am just very pleased that an instructor has taken the time to teach a student to lean the mixture, most of them seem to think that the mixture is an engine ON / OFF switch.
Sadly there are instructors who teach students to lean as soon as they reach cruising altitude, nevertheless if it's only 2000ft. I bet the mechanics are more than pleased when they hear this...
Originally Posted by B2N2
Climbing 30 kts above Vy removes the extra fuel requirement which allows you to lean in the climb as soon as you leave the pattern.
Unfortunately most of the spam cans out there only climb at one speed and have no equipment installed for EGT and CHT.
Given the topic is PA38, the Vy+30 would be 100 KIAS, which is 5-15 KIAS above average cruising speed of an PA38
