Does anyone know how to access the fuel idle adjustment screw? The carb has three covered access ports on the top rear throat which on some other similar carbs have a lean/rich adjustment screw. I can drill and remove the factory plug but I am not sure which of the three in a row plugs covers the screw. My mower is running lean at idle and adjusting this screw has help my other mowers with the same issue yet they were not covered at the factory. Thanks.