172 28mm dell bogging plz help :)

hi every1 i have just fitted a 28mm dellorto to my runner 172, so far atomiser is 268, slide 40 needle d24, and idle is 40 i have tryed 102 jet 108 112 and 120, all seem to run ok at 1/4 throttle but die as soon as i snap the throttle back, the 120 runs ok to 1/4 throttle then when i snap throttle back it seems to jolt and bog for a second or 2 then will start to pull but seems like its very heavy and deep reving when it pulls. any idea what way i should be going with the jet evern higher than 120 or lower that 102 ? i was running the standard 20.5 with open filter and scorp exhaust with a 98 jet and that run fine.