Just had my ZX9 re jetted and set up on rollers on Friday.It seemed to be fine whilst there and i was told it was very lean as it still had the
standard jets in it.
But after getting it out for a blat today it is now coughing and spluttering almost like a misfire when you give it the gas at low revs(sub 5k) at
high revs it runs fine...
It isn't a dyno jet kit just larger main jets, plugs are very light almost white on electrodes and i cannot see any obvious air leaks or pipes
not connected?
I will be ringing the tuner tomorrow but was looking for any ideas really?
sounds lean, especially considering the plug chop.
did you see the dyno run AFTER fitting the kit? you got a print out? - if you post it up then there are some very knowledgable people when it comes to
dynogrpahs - can identify the issue pretty quick 
Back firing would also be a sign that its lean, not sure about the fueling issue though - kinked/obstructed fuel line?? worth a quick check.
i'd get back onto the tuner and get them to sort it out - unless you've had a "fiddle" 
No print out as its not really a dyno as such, but lets say they have many years experience at tuning...
As it was only the main jets that were replaced is it possible that there is not enough fuel at low rpm now? or is it that there is too much...
its incredabley difficult to give a diagnosis over the net, well - unless you had the print out of the dyno run. 
plug chop is your only indication.... and they are not an exact science as they only give an AVERAGE indication, rather than a specific for the
relivant rev range.
Unless the guy has REALLY buggered up the jets (i.e. put SMALLER ones in) then it seems unlikly that they are to blaim for the low end stutter.
I'd check your fuel lines as a first point of call.
You prolly know this, but you CAN seize an engine if it is running too lean 
were changes made to the air side of the equation?
Definately had bigger jets fitted (180) without any air intake changes.
I will have a look at fuel lines but again no changes were made,,,,