Originally posted by warpig
it's the spray bar adjustment.. it moves the venturi position back and forth for different air/fuel flow patterns.. makes minor adjustments to rpm gains... only for very experienced tuners.. you could ruin your engine if you don't tune the whole assembly correctly... easily throw it into a lean setting...
It actually controls the middle range RPM and fuel consumption. The spray bar more inward will lean the middle range RPM and consumes more fuel.