Engine running too fat

Hello, everybody!

It would be nice if someone had their experience for this
Problem set.
Has the following phenomen,at the time of registration of a KLR
System detected during the extended exhaust test
that the CO value ( was 2.5% ) did not go down.
Target value for extended exhaust gas test 0.1%
The lamda value was o,790 ( target 0.97 - 1.003 )
With such a value, the engine runs too fat.
Does any of you have an explanation for this?

Greeting:Hajo