The rear throttle-body stop screw will be used to set the minimum air rate and throttle angle for this throttle body. From the factory, they are capped. Whenever drilling or grinding, cover the throttle body with a clean shop rag to prevent metal filings from entering the engine. Drill down at a slight angle above the Welsh plug and, with a small punch or chisel, remove the cap to allow access to the adjustment. This is usually not required on the front throttle body, since the adjustment will be made with the balance screw. In some instances, if balance cannot be achieved, this plug will also need to be removed.