I need to lower idle speed, factory set at around 1750 but would like to set to below 1300. One place I read on B & S website says cast iron models should be set to 1250. Mine is cast iron model #386447-0024-G1. Downloaded manual and it says do no adjust any carb settings. The only screw I see is probably the idle adjustment screw but the plate is not contacting the set screw. If I turn the set screw in it will only increase RPM's. The various springs and linkages are holding the plate off of the screw. Any way to lower the RPM's?