I've got several G90s and love them, but the mid-range on all of them is still a bit rich. When tuned for a nice reliable idle and a few hundred RPMs short of peak at full-throttle, they still 4-stroke from about 1/3 to 2/3 throttle.

After reading the FAQ about tuning ST engines I tried rotating the spraybar assembly as per the instructions but this has had absolutely *no* effect -- even after methodically moving it in about 2 degree increments through a total arc of about 40 degrees and re-tuning the idle/top-end needles each time.

Is rotating the spraybar supposed to richen or lean out the mid-range? The FAQ doesn't state this and the effects (at least on my 3 engines which vary from 1 hour to 30 hours running time) are not obvious at all.

Lots of people seem to complain about a fat mid-range with their STs and I notice it's quite hard to make precision throttle adjustments in that 1/3-2/3 throttle range when landing a fairly heavily loaded plane with a G90 up-front. The fat mid-range means that changes in throttle position (even quite large ones) involve significant lag -- producing a lot of smoke and burbling before any change in RPMs.