The mix setting on the digifant PB engine is the hexagon set screw on the air filter box. (usually under a blue round plastic 'anti-tamper' cover that's about half an inch diameter.)
I would do all the set up and timing procedures first though as per the famous 'RJ guide', before adjusting the mix, and ideally you will need access to somebody to has an accurate CO test equipment.
keep us posted !
