Why does the enricher circuit make more power, even when warmed up?

[posthuman]

Why does the enricher circuit make more power?

When the "choke" is adjusted into a very exact position near the middle, it gives a distinct boost of power even when warmed up completely, slide the lever past this position and it looses power again.

[DiverRay]

You are probably running a little lean. If the bike is jetted correctly, you should loose a little when the "choke" is on. Check the plug color after a "normal" run, and see if it's correct. IF the plug is closer to white than tan, you probably have some jetting issues.

[Snow]

What Ray said, but also if you have stock jets, they may also be gummed up a little, allowing less fuel flow or perhaps the float heights might be out of spec.