see white paint, that means don't touch it. Factory set for ever. I found one car that someone fiddle the screw, so used a 0.0005" inch feeler gauge and set the fly plate to bore gap. to that ammount, note the 3 zeros to the right of the Decimal point. 1/2 thou. setting. This is so close that water will not pass by valve. and the only purpose is to keep the valve closed and not jam or wear the bore. The intent is zero air flow here. !!!