[dave in australia]

Even though the jets are flow tested to the correct rate, are the ends of the jets the correct shape. The ends of the tube wall need to be rounded from inside to out, similar to cutting a doughnut in half horizontally. If they are square, a small amount of fuel will slowly build up on the end of the jet, and when it gets big enough, will fly off into the airflow and cause a random stammer in the idle. This is not the only cause, but just one possible cause.