You don't lean at 2000' MSL fields. The question is where do you start. We can argue that as a gray area, but I told you what Lycoming and Continental said. Lycoming says not below 5000. Continental says not below an altitude that gives you the continuous cruise power setting at your takeoff power (which is nebulous but is probably a DA of 4000-5000'.).
There is some citrus mixed in with the apples here.
How is field elevation even relevant? I lean according to
density altitude; that's what determines power output and aircraft performance. As mentioned above, I can and do lean for takeoff, even below 1,000' MSL field elevation,
if the density altitude warrants it. And in these parts, it warrants it more often than not, because the DA may be several thousand feet above field elevation.
Imprecise language in my C-172N's POH doesn't help. It says, "Prior to takeoff from fields
above 3000 feet elevation, the mixture should be leaned to give maximum RPM in a full-throttle, static runup" [emphasis added]. I submit that more precisely it should read 3,000'
Density Altitude, but the manual was likely written for the lowest common denominator of consumers. The air density at sea level and 104˚F is no different from 3,000' MSL in ISA conditions.
I know (after flying my airplane for years in a cool, sea level climate in the Pacific Northwest) that after takeoff in ISA conditions at sea level with full rich mixture, the EGT of my hottest cylinder stabilizes at 1290 degrees. As I climb to altitude I just periodically lean to keep it at that same 1290˚ all the way up. No reason for it to be richer than it would be with the red knob all the way in at sea level on a cool day, and there is plenty of reason not to sacrifice the performance by flying over-rich. If the density altitude is higher at takeoff, I'll just lean to that same 1290˚ happy place. In normal cruise-climb oil temp stays well in the green, and CHTs are all less than 370˚. The engine is past mid-time; compressions are high, oil consumption is low, and plugs don't foul.
1000’. Man you guys might get a nosebleed. 
