you have a MAF. to tune one area of fueling only, you find the particular range of MAF airflow where the correction needs to be made (you can datalog for that). then you increase that value to richen the mixture, or decrease it to lean it out. should be done by percentages (take the value *1.03 for a 3% increase in fuel). when you are finished, you have to view the MAF table and make sure the line has nice smooth transitions.