ARF...finally sorted my carb issues...
First I had a bogging down while tipping along at low revs...open the throttle, and nothing ... for a few secs...then start to accelerate away.... turns out to be a clogged pilot jet...makes sense, since pilot jet is helping at low revs, not just idling, and wasn't working properly, but once main jet kicks in off we go.
Second problem...revs won't fall back to idle when throttle is shut off...NOT pilot jet, although some experts suggest that running too rich causes this problem. I went down that road and tried adjusting pilot screws...no difference except lumpy idling.
Put pilot screws back to factory setting.
NOT throttle cable, i fitted a new one and made sure it was snapping back all the way. NOT a partly open choke circuit.
Other expert points out that shutting the throttle should drop all needles into main jets and close them SMARTLY. If one needle is not falling for some reason (diaphragm damaged/not seated correctly or some tiny obstruction) then there will be a delay in revs falling.
I took off the carbs, and without dismantling them completely opened the tops and made sure the diaphragms were seated correctly and the sliders were working smoothly....BINGO..! Blip the throttle and she revs up and falls back like a good FZS should...took it for a burn and experienced bliss of perfect throttle response....this video was a big help -
thanks for the comments and advice