Like others on here, I'm struggling to adjust my 715 holley and trying to follow the suggestions made in other posts on tuning. The carb I'm using is an 80's reissue (1985 Julian date) that I thought had a fuel level sight plug except it's on the primary metering block, not the fuel bowl. Taking the bowl off shows that the plug hole casting is not open to the fuel bowl and clearly not a sight plug. A holley schematic/parts list for a 4150 (only picture I could find) names this part as a "spark hole plug"! Seems like a curious name to give a part on a carb filled with gasoline. So does anyone know what this is? Why poke a hole in the metering block and then close it up with a plug?