phbh atomiser/needle advice needed.

just looking for some advice about clip positions and how they work with different set ups.while trying to getthe jetting something like while running in I had an av268 with x7 needle in my 28phbh dellorto.starts great and ran great at least for running in.on checking plug colour found it too be very black and think I can safely come down a setting.as I am not near main jet position I figure reducing atomiser size made sense.so as I was on the leanest clip position I put in av266 thinking this would be a touch leaner even on the richest clip position.that was my logic which I now think is wrong as the engine now runs "lumpy" as I get toward half throttle were it previousl ran ok.at this point I open the choke which almost kills it,so I get the feeling I am now running richer than before and not that bit leaner I was looking for.so I am hoping someone can explain the logical sequence when fine adjusting .cheers.