Dont listen to the experts on the Richening. high co is a rich mixture. If
you need to get the co down in the hich ranges either put in a new
airfilter(hopefully done already) or open the airbox and readjust the spring
gear about two  clicks stiffer thereby fooling the ecu into leaning the
mixture. Then readjiust the idle co screww to obtain the desired mixture.
After the emission test return your spring to approx 2.5% mixture as this is
ideal for stochiometric performance setting.Good luck.Ed