If you read any of my posts you should understand (at least somewhat) how to use the gas concentration data on your test report to analyze your emission test results.

It would help if you post the numbers and your analysis.

Why are you leaning it? You want the idle duty cycle to average near 50 percent. (It should fluctuate, and the "average" is about halfway between the high and low meter reading fluctuations.) I like to set the idle average mixture slightly rich (meter reading range fluctuation between 50 and 55 percent, for example) since cold starting is better, and this is okay if the 2000 rev duty cycle average is within ten percent. Fifty percent means that the base mechanical mixture is right at stoichiometric, so the control system spends as much time richening as leaning to maintain a stoichiometric average.

If you get the duty cycle too far from 50 percent the system runs out of control authority to maintain an average stoichiometric ratio, and there won't be enough free O2 in the exhaust for proper catalyst reactions.

Too lean a base mixture can fail emissions just as surely as too rich a mixture.

Duke